I wouldn't bother upgrading to to 270 you won't see any preformance gain with it.
The Athlon II x4 620~655 or if you can find any of Phenom II's like the PhenomII x2 555 or quads like the PIIx4 840, 850 would give your system a real boost.
Yeah your going to have to update your BIOS to run these cpu's but its well worth the risk
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PII 1100T (Extinct)
Asus M4A78T-E (should be Extinct)
4Gb of Corsair XMS3 1600Mhz DDR3 (Going strong)
2x1GB 5850's (On their last lags)
Corsair HX850W (Awsome)
NZXT Phantom case (too ***** big)