Try using perfmon to correlate the stutter to points in the log. It seems reasonable to me, like others have stated already, if you are capping out on ram you'll being using page file which will begin R/W to your drive.
In perfmon you'll probably want:
Memory > Page Faults && % Committed Bytes In Use
Physical Disk > Disk Bytes/sec && % Disk Time
Paging File > % Usage
See what those counters show you. You might also change the duration in properties to something like 1000 so you can see a longer history. I could have a couple wrong counters but I think those are the going to be the most useful.