WFM computing speed

While doing WFM the first 15000 iterations is pretty fast ( depending on speed of Cpu) but the last 500-1000 can take forever without using any of the available resources of the computor. I se that especially if doing 20 WFM at the time the Cpu core usage pretty much goes down to nothing if all of them are closing in to the final 500 and it takes for ever. Memory usage are not more then 30 -50% so it has nothing to do with that either. It is the same on both Xeon and Core i7 and the different operating system. This also apply to some of the Robustness test that  take along time without using resources available so i guess this is connected somehow.

I am getting exact the same scenario as Mabi. The Walk Forward Matrix (simulated type) test slows down considerably in the final & remaining <1,000 running test number. I am thinking of upgrading to 22 core CPU but not really sure if that can ultimately solve this. Anyone please advise any work-around to improve the system? Thank you.