Kerbal Noob

I know this is an old thread, but I just bust 1910m/s which is some way above anything here, with stock parts, straight and level on air. I used Rapier's with a single pre-cooler, they are fine at sea level. The problem is always heat. So pop Heat Shield (10m) on the front. Don't open it. Leave it closed. It makes a nice cone for you to fly behind. Now power is the issue ... I don't think busting 2000m/s is out of the question.