You need to use more memory when you run linx to get real stress.
Also, you should boot diagnostic mode when running linx for best results/stress.
Start -> Run -> msconfig -> click the diagnostic mode radio button and click OK -> Restart
To undo it, follow the same steps and choose the normal mode radio button and restart.
For HT on and 12gb, test the 9216MB problem size. 5120MB at least...