Honestly it depends what your doing?
In the macbook the i7 is about 10% faster than the i5 and the i5 about 8% faster than the M3. The i7 is roughly 10% slower than the 3.1ghz i5 in the 4 port macbook pro which is the full fat mobile chip. The 2 port macbook pro has a lower watt cpu than the 4 port.
The 2.3ghz seems to be a bit of a rough diamond in the pack. Although its lower watt, the performance is excellent and for some reason it performs better than the higher watt 3.1ghz i5. There have been some heat issues with it tho, as the thermal architecture is different for some reason.
2.3ghz 2 port MBP
https://browser.geekbench.com/macs/414
3.1ghz 4 port MBP
https://browser.geekbench.com/macs/415
Obviously these are synthetic benchmarks that only run for 1-2 minutes meaning throttling doesn't really come into the equation. If extended periods of CPU intensive tasks are required then the higher watt CPUs will perform better. How much is anyones guess depends on task.
At the end of the day will any of these processors feel that different day to day for normal tasks, I think not.
This is the issue with the current tech, its got so good there is very little difference between any of the dual cores from the 12" macbook and all the 13" variants of the macbook pro.
You can spec a macbook up with the i7 16gbs and 512 for £1850 (without discounts) yet similar spec macbook pro will cost £2400 and they will perform very similarly. Ok you get better port selection which is the downside, but if you dont need it then the macbook is a far better machine for a on the go machine. If you only use it in the house then weight may not be an issue, but then why not spend the same amount and buy a 27" imac... £2400 would get an high end imac that will trounce any of the mobile options.
Hopefully 2018 will see a much bigger difference as the 13" is likely to move to quad and the 15" hex. There will finally be some differentiating factors that actually warrant the price difference.
If im completely honest the 2016 and 2017 13" MBP is completely void, the performance for £$ is poor and apart from ports and the touchbar it makes no sense to me as a purchase. If anyone is serious about a mobile workstation the 15" is far and away a better choice, dedicated graphics, quad CPUs bigger screen etc Its only 10% more than a high end 13" and the difference is stark.
If the 13" gets a quad in 2018 then it will be a no brainer over a macbook, but currently the 2017 models are a bit meh in comparison.
The 13" used to be a great option because it was smaller and had the benefit of the retina display. Now the macbook exists and has the better processors, retina display, far smaller and lighter and offers not dissimilar performance on the high end. The main draw back is the port which is a ball ache.
Is it worth paying the extra for the 13" thats person to person decision. I would rather have the weight difference but a TB3 port would mean you could use more devices at once with a dongle over usb-c which has power draw and bandwidth issues.
Now the Y chips have been set back into 2019 I doubt there will be any updates to the macbook, there isnt enough to warrant it. A TB3 port would be fantastic and make the device so much more usable. That one thing isnt a big enough splash to update the machine for 2018.
There is very little day to day difference between the low end macbook pro and a 12". The main thing is the 12" has no fans and its a very low watt CPU so for extender periods of high intensity work the macbook pro will be a better machine, no doubt.
If your doing normal day to day tasks and dont necessarily need ports to plug numerous devices its a wonderful machine. Super small and light, no penalty to take it anywhere. I now take mine everywhere.
I have the base model 2015 and its the slowest (on paper) machine apple has made in years yet it is extremely capable. HS runs no problem at all, I can run lightroom at an acceptable pace. Apart from video editing, lightroom is probably one of the more cpu intensive programs, adjusting exposure can get the cpu up to 5-600% at times. Seems to handle it adequately, it performs similarly to the Mac Pro in my sig which is impressive. Safari is also excellent, so is word and excel. The fact its a 1.1 and benches a paltry 2500 and 4500 the actual experience is fantastic.
So basically it depends what your doing, for the above its excellent and I would say day to day thats the workflow of the majority.
On the other hand if I had to use it full time for work, I would be dissatisfied. These are not workstations they are day to day media consumption devices, that are capable of doing bits of work. This is how I use it, edit a few images, data transfer etc while im out on location or out of the studio and when I get back edit on a workstation. Great compromise for me.
Your mileage may vary. The newer gen are far faster than mine. So I think if my experience has been good then they are only going to be better.
It also depends on your situation. I use high end workstations to do actual work and like to have a light travel option that can do most things on the go. Im a photographer and my photographic gear is heavy enough as it is so the light laptop that is 1kg is lighter than the majority of my lenses. It can edit in the field, get a few images to a client, email etc has a full OS.
The reason I like the macbook over an iPad because you still cant do much with them, especially data management.
If your someone who wants one machine its difficult. The 13" is expensive for what it is and isnt much more powerful but is noticeably heavier and thicker IMO and the extra inch doesnt make the difference worth it. The 15" is impressive in terms of what it packs for its size, but its still unwieldy on your lap or on the sofa/bed, hard to fit on a train or airplane fold out table and you cant get away from the fact it weighs twice as much. But you can slip it into a full desktop setup with ease and be content with it being a mobile workstation.
Then there is the macbook which is a great machine but is a difficult one for many to get their heads around the single port... Apple has not made this line up easy for anyone to choose a product who actually dig down into the numbers. The rest is gimmicks, not professional solutions.
Buying a 13" MBP doesn't necessarily give you a pro experience like it used to.