I wouldn't recommend a mini t for high speeds. I never really spent much time trying to get mine super fast, but even trying to get to about 40 mph was hard enough not flipping it on its back. It was hard to keep in a straight line, it always swerved all over the place (maybe just my setup), and the transmission and diff didn't seem that strong (don't know what upgrades there are). People say MT's are hard to control at speed, but mine have been easier than the mini t. Oh and I hate working on it, which is probably part of the reason I never got it setup that well, so I got sick off it and it's been sitting for the last year or so.
I say get a semi decent 1/10th on road. Half the stuff you need to do to get mini-t to handle at those speeds will be standard on the 1/10th. Still pretty light, and 1/10th setups aren't that much more expensive than decent 1/18th stuff.
Have you seen this 120mph tc4 with mamba max combo?
http://www.youtube.com/watch?v=46ssL...e=channel_page
http://www.youtube.com/watch?v=zAwSb...e=channel_page
http://www.youtube.com/watch?v=6u7nU...eature=channel
Here's the thread for that car
http://www.rc-monster.com/forum/showthread.php?t=11633