I dont think its worth it. On my setup with radeon 4850 and 2gb of ram the difference between running cpu at 3.4 and 3.9 gives around 3fps difference in Crysis. Considering the extra voltage, heat and stress on cpu, to me thats nowhere near worth it. And i dont think 4ghz e8500 would bottleneck any gfx available on the market atm. Just like r_manic said, if its working fine than leave is as it is.