As far as I understand, for both low and high, the code that implements the key search most quickly on specific equipment is suitable everywhere. Earlier, when I was in the subject and tested the fastest codes for searching were from the author of JLP, due to a long absence, I can not say exactly what the situation is today, with programs that are freely available.
try to quote properly, there is a button for that:
About the options, for any low and high bits the best option is always a GPU program, the real question is what is the best for you budget if you already has a GPU then use a GPU program that fit your needs, if you don't have one, well the answer is obvious you need to use programs for CPU.
Which program? well I don't know check what is working properly and it fits to your needs.
GPU is just parallelization of the process. This is clear. When I was doing tests, something else was interesting. A specific machine, a specific key in the range. (specific task) Load in 1 thread, core. Only the time spent on execution was taken as a basis.
Agree, what wat is GPU depends only from your hend and your brain.