I can't answer any of your questions regarding Intel CPU types and that might be best to be started in a new post.
The Green 753 doesn't benefit from using a MMX cpu while do I believe I've run the Intel MMX CPU's in the Green 753 years ago, but don't recall the details. The 233MMX CPU produces a lot of heat. Best solution for finding the Vcc of any Intel CPU is to use the 5 digit code on the CPU and do a look up to determine the proper core voltage. Such as the 166 MHz Pentium SY016 which I find is listed as 3.4-3.6 volts. I do remember that the AMD CPU's didn't post and I'm trying to remember the details of my tests. I believe there was the need to cut off one pin on the AMD's since they are use an extra pin only found on the Socket 7 CPU. A concern is with these laptops is the watts the CPU consumes, the Green 753 uses a heat pipe to cool the CPU and doesn't have a CPU fan. The heat pipe works well for lower watt CPU's, but can cause a lot of heat buildup under the keyboard. I think it is pushed to the limit with the 166 or 200 MHz CPU's.