I have the lowly i3 Second Generation Dell. I upgraded my memory to the max allowed with my cheapo machine, 8 Gigs. Sonar X3 runs great with it...no need to upgrade at this time.
When I upgraded my RAM I bought genuine Dell Ram 4 Gig sticks....I have had no problems with them at all. They fired up right away and have been working for about 2 years now. They were a couple of bucks more money, but worth it...no hassles at all.