as far as the weight in the back if you went with the Emaxx tranny that would give you the same configuration as the new E Revo. It also depends on what you will be doing...if you are going to be racing where weight distribution is more critical the Emaxx style is better...I used the stock Revo tranny in my conversion I mostly bash in very wide open areas and for me it works great...I cant even remember the last time I used reverse or my brakes......lol
I think you should get the new E-Revo and convert it to Nitro!
Seriously though, I'd convert the 3.3. I have the new Erevo myself and I'd rather have the metal chassis that doesn't have the stupid battery boxes limiting your battery selection and battery vendors.
You'd have more fun converting it. Or, at least I would.