Shooting for 100 mph in a buggy...wow. As I said, the mugens are built like tanks and the associated makes a great buggy as well. Seeing as you are looking to go as fast as possible...I suggest looking at the weight of the ones you are looking at. The mugen for example is heavier than the associated...etc...Both buggies are super easy to convert.
Mike sells a complete conversion kit for the associasted...
http://www.rc-monster.com/rcm.php. Mike's kits are super simple to do the conversion with.
1. MBX-6 T8 1900KV, RX8 ON 4S
2. MBX-5T 1520, MMM ON 5S
3. MBX-5 ONROAD CONVERSION 1515, MMM ON 5S
4. MRX-3 ON ROAD CONVERSION 1512, MMM ON 6S
5. TEN T 2650 T8, MMP ON 3S