I have word that Hitec has made a 7.4vdc version of the HS-5645MG servo! Dubbed the HS-5685MH. From the pricelist.
HS-5685MH High Voltage, High Torque, Metal Gear, Digital, Dual Ball Bearing (168oz/in, .18sec.,1.55x0.77x1.48") ETA JULY 2010
I already have them on order. They have a street price of $56.99. That’s only 2 bucks more than the 5645! Happy dance! 
Ooo. just in time for my birthday. sounds very good and very well priced. This is great news for all those lipo users here. keep us updated. 
http://www.hitecrc.de/store/image.php?type=T&id=21451
Based on the one online store that listed it’s specs it has 182 oz/in at 7.4v. This sounds like the 5645 but with a voltage regulator for the electronics so it can safely run at 7.4v. Makes sense. They should change all their old servos over to 7.4v compatible ones.
