A few issues with this,
Firstly the chips are 2 generations (1 for the 15 inch) out of date so despite your nonsense and the difference being only about 10-20% new chips are much better performers which give far better battery life and are far cooler.
Secondly and more importantly in the case of the 13 inch the graphics are about 100% better and the 650M dGPU has issues with failure, so a 3 year old 15 inch is looking like a bit of a timebomb.
Thirdly the PCIe SSD's are a lot faster than SATA 3, thunderbolt 2 allows 60Hz output to a 4K screen thunderbolt one does not, forcetouch is now becoming an apple standard.
Fourthly the OP clearly cares about size and weight and the rMBP is far slimmer and lighter to carry around, for both of the sizes.
Fithly by the time you have upgraded the cMBP with SSD and RAM you are almost at the price of a brand new laptop that is not 3 1/2 year old technology.
Lastly and by all means most importantly why would anyone choose to miss out on the retina screens in favour of a more than 3 year old laptop. The retina screens are brilliant, low glare, great viewing angles and Text is like reading print.
The 13 inch is 2 generations and the 15 inch is one gen back, true. However, what I said was not nonsense. And define better performance because the 5th gen actually puts out more heat than earlier generations and is one of the main causes for the smaller percentage in performance increase over previous generations.
The graphics are better in the retina machine for sure and the ability too utput to 4k is great. I also think the display is awesome but not worth it in my opinion to go with the 13 inch retina when I can make a 13 cMBP outperform it for less money. And upgrading the 13 rMBP to the point where the cMBP is no longer a reasonable choice makes the 13" rMBP too expensive for what you get and at that price point I would go with a 15" rMBP. And right now the 15" rMBP with Integrated graphics is only $1849 at Best Buy.
There were some instances of failure but not that many and the 2012 15" is still a better buy in my opinion.
PCIe 2.0 SSDs are faster than SATA 3 HDDs for sure, but that's only if you compare the speeds of an SSD to a HDD. But PCIe 2.0 SSDs versus SATA 3 SSDs is the same. And the benefit of the 2012 is that there are 2 SATA connections which allows for more expandability and the ability to create your own RAID that drastically outperforms the PCIe 2.0 flash-based SSD in the retina machine.
It is slimmer but not that much lighter (only 1 lb). So yes I did read that the OP cares about size and weight but I think the OP also cares more about performance of the machine than it seems by the original post. My original response and recommendations are still the ones that I would make first and then my number 3 would be the 15" rMBP. And that machine weighs more than the 13" cMBP.
And yes that's true that you're "almost" at the price of a brand new laptop.
rMBP: $1,499
2.7GHz dual i5
16GB RAM
128GB SSD
cMBP: $1,454
2.5GHz dual i5
16GB RAM
2 x 240GB SATA 3 SSD
Those prices are pre-tax totals but upgrading the cMBP is less expensive and I think a better investment due to the capabilities of the machine.
The reason why I would choose to miss out on the retina screens is because they are not THAT awesome so that the retina becomes the primary reason to purchase a machine. I get that they are low glare and all the benefits that come with them, but I want a Mac to last as long as possible and for me to be able to do as much as possible with them. That's not to say that I would never buy a rMBP; because I would. I just want them to be much more powerful than the cMBP before I commit to buying something like that instead of buying something that is only an incremental upgrade. Once they have PCIe 3.0 or higher, then I would seriously consider upgrading, but not when a cMBP can have 2 SSDs in RAID and double the R/W of the rMBP.
I have thought about getting another 13 inch pro but I feel lk o either want something really skinny and sleek(nMB or MBA) or a wider screen wit the 15 inch rMBP. You think I'm being to picky? It's only because I have a 13 inch pro but I know the new ones are ALOT slimmer then what I have. I think if I can find a new rMBP for under 1850 I should get it.
OP,
the 15" rMBP with 256GB SSD and integrated graphics is only $1,849 right now and the 15" rMBP with 512MB SSD and dedicated graphics is only $2,300.
So they're both on sale now and if you're leaning at all toward the 15" due to the quad-corinees, then now might be the perfect time.