PSU is not something to be taken lightly with.
A little story:
A month ago I help my cousin OC his GC and CPU and ran stress tests such as Furmark and LinX.
The PC suddenly shuts down.
After further inspection, I see the mobo standby lights are ON, but failed to power up.
So I initially concluded that its the mobo which died out. But the day after I felt a bit rajin and "jump start" the PC using my PSU and magically it's alive!!

So my point is that my cousin's PSU has a similar 'real power' as yours and with similar rig setup as well AND it proved to be unrecommended especially when doing some overclocking.

The glitches possibly caused by instability of PSU in supplying power to your 9800GT, probably the capacitors in the PSU already succumbed to damage after you OC'ed...

Bro, to speculate if the whole system is stable or not, you have to run a 'STRESS TEST'.
This will tell if your system is unstable even without OC'ing. (ask the sifus about this)

At this point, more data is needed bro, please keep on posting.
As for the moment see if the glitches are still available without any kind of OC'ing. This is a very crucial data to figure out what is the problem...