[RandomBK]

Code length will itself become a problem. The instruction cache is limited in size and often quite small. Bloating instruction counts with lots of duplicated code will eventually have a negative effect on performance.

Ultimately, there's too many factors to predetermine which approach is faster. Write clean code, and let a profiler guide optimizations when needed.

[LorenPechtel]

Exactly. Memory access is a major factor in runtime, often more important than instruction counts. And in the vast, vast majority of cases it doesn't matter. I trust the compiler to make reasonable choices, something would have to be deployed at a very large scale before the programmer time of considering such things became cheaper than the hardware savings from doing it. And the vast majority of code simply doesn't execute often enough to matter one way or the other.

Save your brainpower for the right algorithms and for the inner loops the profiler identifies (I did not expect to learn that the slowest piece of code was referring to SQL fields by name!) Ignore the rest.