Which processor version is used in MBP 2017?

The HQ series are the quad cores in the 15" while the U series are the dual cores in the 13".

If you want to edit 4k and you want to do it on a MacBook, then go for the 15" model. The extra cores, discrete GPU, and more RAM will all help.

 

HQ - 4 cores, 8 threads (15")
U - 2 cores, 4 threads (13")

The U-series are almost just as fast as the HQ for single threaded tasks, however if you frequently edit video, the 15" is recommended due to double core count. If you do it rarely though, you can save some money and get the 13". You'll just wait more for exports.

Paid processor upgrades are almost never recommended, the difference from a couple hundred MHz is barely noticeable.

Wikipedia has the exact CPU models for each MacBook Pro: https://en.wikipedia.org/wiki/MacBook_Pro#Technical_specifications_4
If you google the processor model (e.g. "i5-7267U") the first result should be from Intel's database (ark.intel.com) with detailed information for each CPU.

 

For the iMac, the main difference for the upgrade you refer to is that the upgrade option is an i7 with Hyperthreading, so you would get 8 threads instead of 4. Along with a few hundred MHz for the clock speed.
Honestly, for most people the i5 is fine. But if you very often do video editing, or use other multi-threaded software (such as simulation software, code compiling, CAD design, etc.), then the i7 could be worth it.
My usual advice for people asking if they should go for multiple cores/thread, or stuff like 32GB of RAM, is "if you needed it, you would already know it".

 

You will get Hyper Threading with the i7, allowing for 8 threads vs 4 with the i5.

 

The problem with U-series is they themselves are subdivided in multiple performance tiers (with significant differences):

• 7x00U series (15W, lower-tier GPU without L4 cache)
• 7x60U series (15W, higher-tier GPU with L4 cache)
• 7x67U series (28W, higher-tier GPU with L4 cache)

Apple only uses the models with higher-tier GPU.