I think it's important to have both (and indeed, do use both): a blazing-fast development machine for actually writing the code and a slow-as-molasses test mach

I think it's important to have both (and indeed, do use both): a blazing-fast development machine for actually writing the code and a slow-as-molasses test machine (be it separate hardware or a heavily-handicapped VM on the fast machine) for dogfooding/testing the code. With the former, the faster the better; with the latter, the slower the better.