Well I've been looking at running a 2 cell lipoly pack for my mp777 for a while but I was on the fence as to running it unregulated or using the novak 6v regulator. I called airtronics but they said the servo wouldn't last with 7.4v + so I did some more searching and found a regulator made by VXR that puts out 6.7v so I pick up some speed and torque but (hopefully) won't shorten the life of the servo. I picked up a 1000 mah lipoly and regulator from www.teamtaylorracing.net If anyone has any experience with these please feel free to post your opinions. I should have it in and be able to give a review in a week or two. I'll keep you posted.

I've got the 5A regulator. 1A isn't going to be enough for a car with two decent servos I think, as one of them can pull as much as 3A. They advise the 1A regulator only for electric touring cars that have one servo.
6.7V will be perfectly fine for most servos. A freshly charged NiMH pack can put out more than 7V. LiPo without a regulator would be overkill indeed, because a freshly charged LiPo pack can put out more than 8V.

I got myself a 240mAh pack for qualifiers, and a 500 and a 750 for finals (depending on runtime). Only tested it in the dry so far (still winter here) but it's amazing. The Servos are faster and stronger than with a NiMH pack that isn't freshly charged. And it's just amazing how light these cells are.

If you get the 5A regulator, just make sure you run PCM or Spektrum, as they discovered that it can interfere with FM and AM. They're developing a new 5A regulator now that doesn't have this problem I hear.

http://www.rcuniverse.com/forum/forumid_84/tt.htm