[Batfish]

R00ST,
Based on what you are looking for, my first suggestion would be to take the good HV-Maxx you have and get the right gearing for it to run in the Revo.
Here's why:
1 - Climbing. If you really want to do super-low-speed climbing and crawling, the HV (or another sensored system) is the best choice. Although both the Warrior 9920 and the MGM controllers can accomplish low-speed running, neither will accomodate the rock-crawling speeds as easily as the HV. This is based on my own experience with both makes of sensorless controllers.
2 - Speed. You didn't say you were looking for any speed records, and I'd expect (with appropriate gearing and cooling) the HV could get you in the upper 20s for speed.
3 - You've already got it. With an investment if $20ish in different sized pinions you can find out if the HV will work for you.

The sensorless systems easily blow away the HV for speed and are definitely preferred here for bashing and racing. They can also accomplish decent, cog-free, low-speed movement. The low-speed of the sensorless is not the low-speed you'd typically use in crawling.
That said, you could still (most likely) gear a sensorless system to accomplish some casual rock-crawling, but my personal choice for that task would be the HV.

Essentially, you'll need to weigh your choices. If you want the best rock-crawling capabilities, you're probably better off with the HV (geared and cooled appropriately). If you want speed and bashing power, you're surely better off with a sensorless system (also geared and cooled appropriately).