i dont know whats faster but the savage is WAY MOR DURABLE. i saw this one vid of a jump the savage did. it was MASSIVE, the thing prob went the height of a 2 story house of the side of a 10foot-15foot hill and landed still running fine and after the jump he started going top speed in a parking lot (FAST). so if i were you i would go with the savage. i think the SS 4.6 is the best deal (excpecially with that big block engine (does wheelies with no prob, thats how prowerfull the engine is), but i think it only comes in a kit. so if you are willing to do a kit get the SS 4.6 but if you want a RTR get the normal HPI 1/8 Savage 25 RTR, and if you are willing to spend the extra money get the special edition.
i dont know what the best stadium trucks out there are but if you goto the truggie forum you can prob ask some of them some questions about the factory truggies. as i said before i have the hpi nitro mt (its the old version and if you get the mt2 i can tell you it is a good stadium truck from experience. It has A LOT of option parts and hop-ups plus you could put a more power full and faster engine in it late down the road if you want.

Hope this helped!

i dont really know what goes faster though. i think they are pretty close speed wise.