Memtest 4.3.7 running slower and slower as more passes run

[perdrix]

The first pass (pass 0) on 20GB ram runnning with 2*Xeon E5345 (2.33GHz) took around 2-3 hours. It is now running the eighth pass (pass 7) but has just passed 45-1/2" hours of run time

Had it been linear with time, I would have expected to have got here in just over 24hrs. Something wrong here?

Thanks
Dave

[David (PassMark)]

The first pass is designed to be faster, as a quick check.

But passes 2 to 7 should take roughly equal time.