Re: cpu cooler for e8400
The Noctua is a fine heatsink, i would bet you would be able to hit 4Ghz, although nothing is guaranteed in overclocking. Full load temps average 55-65 for such an overclock on an E8400, but this also depends on your case. Those temps are fine for the cpu, but if you're uncomfortable with them get the TRUE 120 and chuck two fans on it.
If you go with the Noctua, buy an extra fan for Push-Pull as it only comes with one fan. The same fan that the heatsink comes with (P12-1300 120mm) is only 27 bucks and will help cool your cpu by a few degrees.