Hmm.. Dual channel made the difference for me, but I am running a much more recent setup. In my opinion, better save up some more and upgrade the CPU. Sell this one and get some bucks out of it, save up some more and orient yourself towards a more recent setup. If money is a problem, keep the DDR3 RAM.
Also, if you want to convince yourself, get a stick of RAM to make it dual channel and return it to the seller if there is no major difference.