Previously this was the double the CPU count because:
- Modern CPU's from AMD & Intel support SMT/hyper-threading which
present twice as many cores, doubling again has little to no benefit.
- Using 2x or 4x the number of physical cores number can use a lot of
memory on systems with many cores which are becoming more common.
Show a percentage output as the numbers weren't especially meaningful.
Also use default arguments for credits generator so no arguments
are required to generate all-time credits.
