High Jitter Spikes

Hello all,
Long time viewer, first time poster here.

I'm at my wits end here with this PC. I got Linux CNC 2.8.2 on an old Dell Optiplex 380 with 4GB RAM and a Core2Duo E7500. I messed around with the RTAI kernel to see what I could get the jitter down to, and I was quite happy. I was under 10us with the RTAI kernel... for about 5 minutes. After that, the jitter skyrocketed over 1ms! I'm not sure what gives here. I'm planning on using a Mesa 5i25 + 7i76 combo. I have an nVidia Quadro GPU in as well.

Things I've tried:
isolcpus = 1   -Not sure if this makes a difference, certainly didn't hurt
2.8.2 with RTAI kernel -Definitely reduced the jitter when using Firefox, but still random spikes over 1ms at times.
Disabling every power saving feature in the BIOS

Is there anything I'm missing here? Should I just not care about the jitter since I'm going the Mesa route anyways?

wiki.linuxcnc.org/cgi-bin/wiki.pl?TroubleShooting

forum.linuxcnc.org/18-computer/19125-faq-some-latency-solutions

forum.linuxcnc.org/18-computer/19022-faq-the-latency-problem

forum.linuxcnc.org/18-computer/25927-red...lticore-pc-s-success

Only going to give links, as it could be several issues. The above should give you something to start with.

ALittleOffTheRails wrote:

wiki.linuxcnc.org/cgi-bin/wiki.pl?TroubleShooting

forum.linuxcnc.org/18-computer/19125-faq-some-latency-solutions

forum.linuxcnc.org/18-computer/19022-faq-the-latency-problem

forum.linuxcnc.org/18-computer/25927-red...lticore-pc-s-success

Only going to give links, as it could be several issues. The above should give you something to start with.
 

I'll give these a shot, thank you. I'll come back after I exhaust all options here.