At that resolution I wouldn't worry about it.
However, I would DEFINITELY start looking at combos (CPU/MOBO, and DDR3 if you haven't got 8GB yet) to bring your CPU performance up.
The PhII X4 is a fine CPU, I have an X6 and like it very much (it's in a media box now, not the most efficient use, but it works well).
IIRC the 920 tops out usually in the 3.2-3.5Ghz range outside of very rare exceptions, and that's starting to show its age in some titles.
You could check if your board will take a 6300 and just go that route for the easiest solid upgrade, or :
Look for a used Mobo+2500k, get a $20 air cooler, and OC to ~4 through 4.5Ghz and you'll see massive leaps in minimum and average FPS in stressful titles. It's the exact move I made a while back, I took a PhII 955BE @ 3.8, jumped to Thuban @ 4Ghz, then after seeing minimal gaming improvements moved to a 2500K. That was a BIG leap. In fact I've upgraded a couple of times since then and gaming didn't really boost further.