The RPM front bumper is great. It can take a lot of abuse. It also has a front skid plade designed in to it. I have found it gives a good bit more protection vs the stock.
I think the Hex is a 12mm. But I could be wrong. Why do you want aluminum? I have never had an issue with the plastic units. But I also run aluminum rims from
www.rc-parts.com about 97% of the time...
On the pipe... I run the Traxxas Dual Chamber Resonator with my RB V.12 it really brings the motors to life in the mid to high rpms. I have also tested it with the 2.5 and 3.3 it worked just as good with them. My favorite pipe was one from Novarossi. But that pipe is now out of production... I use it on my basher...
the vantage pipes are killer looking, but I have never tried one.