I'm having the same issues, the logs say absolutely nothing regarding what would be causing the issues, only the usual waypoints etc etc. Even with just one client running I've tried 60/60 limits, no limits, etc etc etc. Its fine when I'm not using DB but as soon as I hit start every 15 seconds or so the fps will drop down to 25, and it will be very jerky. After spending 12 hours trying to fix this issue through testing in VMware and ISBoxer...I've come to the conclusion its not my machine.
PC is a 3770k, 16GB DDR3 1600Mhz, 120GB SSD, ATI 7850 (even tried in crossfire as I have another card), Z77 Mobo.
Edit: Forgot to say that CPU load is under 30% with plenty of free RAM available