<< "btw would the gc68 with the ys-tech 48cfm be better than the sk-6 with delta screamer? " >>
You guys gotta look at it like this, the GC-68 is Alumminum, and the Sk-6 is copper. It's going to perform better then the GC-68. Obviously. They both have similar shapes, but the Sk-6 is better.
The GC-68 is a good budget fan. I wouldn't use it for overclocking, thought you can. For 13 dollars you can expect a nice and quiet heatsink/fan that will do more then the retail hsf by far. Like i Said, it's more of a budget heatsink. You can overclock a little, but if you want to oc, i would pick up an alpha or something copper. Sk-6, Golden gate, Some vantec heatsink, Dynatron heatisink, ...on and on. Look for something that is proven. You can pickup a decent copper 60mm heatsink for under 20 dollars.
-JokerF15