RE: Rx battery questions
I have 4 of these packs (5-cell version) currently in service and a couple more waiting for a home and they work great.
Some older and/or less expensive NiMh batteries do supposedly have higher internal impedance which can restrict current flowand cause a voltage drop in high demand situations but I haven't found that to be the case with the Hobbico packs. They seem to work really well for what I've used them for.
I'm running a single pack in my TF P-47 and my Cap-580 and dual packs in parallel on my Yak-54. I've been very happy with the performance in each plane. If you are really concerned though, running the two packs will not only increase capacity, it will lower the overall resistance along with providing a little redundancy.
A high capacity 4-cell pack will also work just fine as RCKen pointed out. Either way you'll be fine.
On your FW, how many servos are you talking? Typically on a smaller warbird you have 2 aileron, 2 flaps, 1 elevator, 1 rudder, 1 throttle and 1 retract. The flaps and retracts servos really only operate twice during a flight (up once and down once) so the power demand is slightly higher but not dramatically more than a typical sport plane. Where you really run into problems with servo drain is the monster digital servos on large aerobatic planes.
What FW do you have?