What do the BOINC benchmarks show?

Are you running 64-bit Linux, and if so is the UGM app 64-bit? i'm guessing that the Windows app is 32-bit only (I have no Windows machines on which to check!)

I have only done comparative testing on FAH2 jobs, but the average times for 32-bit FAH2 jobs on a 32-bit Linux virtual machine on a 64-bit Linux host are about 25% less than 64-bit FAH2 jobs run on the host itself. That makes the 64-bit apps about 30% slower. This observation is based on over 150 tasks of each type.

It wouldn't surprise me if the same is true of quite a lot of applications - it will depend on compilation options (choice of arithmetic precision, &c), optimizations and all sorts of other things - 32-bit and 64-bit apps are rarely identical in performance.

For what it's worth, the only platform I have that tends to get UGM jobs has an i3-2100 clocked at 3.1GHz, and it typically takes 3.5 to 4 hours to run a single 64-bit Linux UGM task.

I run only Win7 64-bit machines, and on an i5-3550 (3.3 GHz), I have been getting slightly under 2 hours per UGM WU (7.28). Note that that is on a full Ivy Bridge core however, so a virtual core would probably run about 3.5 hours or a little less as a guess.

I will be putting together a Skylake machine later, with Linux Mint 18, so will be interested in seeing what works best on what OS.

EDIT:To check the effect of hyperthreading, I ran UGM 7.28 on all 8 cores of an i7-4771 (3.7 GHz). They came in at exactly 3 hours, so this project does well on virtual cores. I think I will leave it on my Win7 64-bit machines.