Questions about MacBook Pro hardware

In regard to your heat question: when you are comparing the same CPU running at different speeds then the faster CPU will run somewhat hotter than the slower one. However you cannot safely compare two different CPUs (say the i5 and the i7) and make the same assumption. Furthermore, you need to look at the entire package - heat isn’t generated just by the CPU. If you compare two the same Mac computer, one utilizing Intel’s integrated video and the other a discrete video card it is possible that the computer with the discrete video will run hotter.

In terms of your questions about longevity: you are asking us to speculate about the future in ways that we cannot. The whole idea of developing CPUs with multiple cores is amazing but the hardware technology of multiple processors is at least one generation ahead of the software technology. If programming languages (and programmers) had kept pace with the hardware technology a dual core processor would be twice as fast as a simple core processor - but it isn’t. I’ve heard it said by several programming language developers that compilers tend to reach their maturity just about the time the CPU they were developed for is replaced by a newer model. I used to buy the best computer I could afford hoping to make it last a long time but about 10 years ago I changed my thinking: I now buy the low end model expecting to replace it frequently (and being grateful that it tends to last longer than I expected).

Resolution does tend to have an impact on performance. The retina models have a native (or preferred) resolution and if you change from that resolution the GPU has to work harder to adapt the output.