I have to admit I overlooked the 4GB vs 8GB in your post. But I still stick by my suggestion tbh.
Having run an i7 with 6GB and a i5 with 8GB as my main systems in the past, I'm happily sitting here running 4GB of DDR2 on a C2D E8400 and haven't really noticed sod all difference.
Get the Mushkin, clock the bolax off it and enjoy a very nippy PC