I had a gutted stock end can on the bike. It was very loud, fun to blip and ride with in the traffic, but rather obnoxious really, also you'll need to jet the bike after it's done (AFAIK). Don't do that. It's lame.
I recently acquired a full yoshi RS2 system, like the one bus has, and it is freaking awesome

my bike is an E-model, so there wasn't a massive difference, but it has smoother power delivery, a much nicer sound and a lighter front wheel. All round win. That being said I don't think I would've shelled out the R4000k for one, I got it second hand. And yes the subframe mount points are slightly diff, but not that bad, made a plan.
The FCR carb is stock on the e-models, hey?
If you don't know there are 3 DRZ models, basically the same with a few differences:
E- enduro, sometimes no subframe, the FCR carb and a better header pipe. Also comes stock with shorter gearing. The hooligan offroad model
S- the diet coke of DRZ's, longer gearing and a less aggressive carb. Bus has one that he has made into a monster, new carb, header pipe, changed gearing, etc, but stock they are (better) for longer distances and slightly calmer riders?
SM- super motard, RMZ shocks and bigger disc brakes front and back. It however has a much worse carb on the bike, so it's a bit soft standard.
But bus and sidetrack know much more about this than me.
Apparently though the very recent (2008+) do not actually need the automatic cam chain tensioners, I am not sure.