I'm not going to spend any time getting into the details, how I arrived at these conclusions, etc. I'm sure plenty of you will disagree with this. That is okay.
The recipe for a fast Droid, simply put, is:
1. I am highly suspicious of themes. Stock is faster. I cannot prove this.
2. Non-stock "launchers" are very bad, at least right now. Don't use anything called "Launcher" or "Helix". Use the stock "Home" app. If you run CyanogenMod, you can install the stock Home from ROM Manager. Try it.
3. Overclocking appears to kick things up a notch. I'm on a 1.1ghz 5-slot, standard-voltage bebit kernel right now and all is well. I'm going to downgrade later today to the stock clockspeed for comparison.
4. App/task killers are bad. This has been discussed to death. Put some faith in Linux and Android.
I'll probably get buried for this, but yes, I'm essentially telling you that Motorola, Google, and Verizon pretty much got it right. Almost everything I've installed from the modding community has been a net performance hit compared to the stock system. At this point, the only reasons I remain rooted is for WiFi tethering and overclocking.