A fully charged LiFe (A123 type) battery is 7.4V - it doesn't stay there very long but the first minute or two off the charger it'll run over 7V. Five cell NiMH or NiCD come off the charger around 6.7V or so. The LiFe packs are running about .5V higher.
I have been running LiFe/A123 type for about a year now. The only area I'd have a concern is with servos that are known not to handle higher voltage such as the Futaba 9254. I would run a regulator in front of the 9254 or JR 8900.
I do specifically buy and use servos that are known good at 7V+ volts now. I have not had any problems with the Hitec, Ace and Align servos that I've been running on straight liFe 2S voltage. If the servos are rated for 6V operation then they are most likely good with LiFe voltage but ask around if you are not sure. There may be folks who have tried running them at higher voltage.