What I am interested in is if I have less hardware does DB3 automatically figure out what hardware I do have or do I need a separate version of DB3 for each hardware configuration?
It'll automatically detect what your hardware can do. The only caveat is that I think it'll force you to restart the program to switch between standard and High Octane mode.
Also, how much slower will the program run with no CPU calculations on the GPU, no AVX, and only two cores?
It really depends on a lot of factors that are difficult to predict until I have something to test. In theory AVX would let it run up to 4x faster, and a GPU at peak can run about 10-20x faster than a CPU, but there's memory bandwidth issues. On the CPU, transferring data from memory to the CPU is often the bottleneck, so AVX might only give 1.5-2x improvement. For the GPU, you have to physically copy the data from RAM to the card before you can do any calculations on it, which can take a LONG time. Which might mean the GPU isn't any faster than the CPU, but it should still let you go much wider (ie: have more bots in the sim).
You should still be more than capable of running a reasonable sim with older hardware. But if you're looking to do a long term experiment, better hardware is going to be worth it.