I also would stick with the e8400. Im using one also, and slightly overclocked.
THe mobo should be upward compatibale for the I series also.
I know my mobo is expandable. But I should see several years with the setup I did.
yeah yeah, my bad, didnt have my coffee.
I can upgrade to a intel core 2 quad though (Yorkfield). Have no need at this point though. And they seem to hold their value, cause the prices are still WAY up there.