Ken,

If you like Futaba servos and want to go digital, you may want to look at the S3152's. At 6.0 V, they may be exactly what you're looking for. I'm assuming that, even though you mentioned a 90 sized four cycle sized airframe, that means you're sticking a glow motor in it. If you're electrifying it, you'll have a lot less vibration which is what really prematurely hurts the servos. A nice full list can be found at http://www.futabarc.com/servos/digital.html with all the specs you may need.

Scott