Eh, I have 2 GB RAM and just the teeniest bit over 1 GB of downloads split between my Downloads and Saved Sims folders, and even with a good processor and video card, I still get lag when teleporting, and I get more lag the larger the lot and more people on it.
I think the problem is crappy programming more than the amount of downloads.
The only real solution is to try to avoid anything over a 4x4 lot, more than 4-6 Sims per household, and the disco lights and blinky floortiles and boxes from NL. Otherwise, learn to love your lag! LOL