couple questions

Which Reverb are you using? A few of us have trouble on playback (not render) with pops and clicks using impulse reverbs like Reaverb, especially with any other delay on the chain. Sir works fine for me unless I have too many in the project. To me it looks like your machine should be fine, I would try a couple of different reverbs, or different impulses and see if that makes a difference. A hint for your drum tracks is to put them in a folder and then you can easily solo the folder track to render a single stereo track of drums if needed. The other way is to solo the 4drum tracks and Render them to a single file.

How do I try dif. impulses? I've read some stuff here about impulses but I don't quite get it. How do I put my drum tracks in a folder? I spent about an hour trying to figure that out today. If I solo the four tracks and render them will reaper just give me a new consolidated track? or a file that I will have to import? thanks!

As far as using different impulses, you download the impulses and save them. Then, say, for example using Reaverb, you would click "add file" then browse for the reverb impulse you want to add. Doing a search on the forums here/and google you will be able to find quite a few impulses. So you use Reaverb or SIR (also the JS Guitar Amp and Voxengo Boogex)and load the Reverb, cabinet, or whatever impulse you want. I had less than 512 available RAM and upgraded to 1.2 and it helped considerably, so I'm sure when you jump to over 2 that should help you out quite a bit. BW already told you how to mix the four drums to one stereo - in lay terms, you could just open a new project and those four drum tracks and render them to a stereo wav. Kjaerhaus audio Classic Reverb (and all of the other Classic Series) is very low on CPU on my end. Using impulses can eat up alot of CPU on my end. I find, that if I have my tracks where I want them with EQ, etc., I might take some FX out of the fx buss and after I "apply fx as new take," which can help save considerable resources as well. Anwida's DX light is great, but it will virtually always shut down Reaper if I have too many other fx/etc. going whereas Kjaerhaus for example will not. I have not tried SIR yet, but wonder if it might be less CPU intense than Reaverb.