I asked the same question of at my LHS; About the same servos. Here are the specs:

S3151($34.99 at Tower)
Speed: 0.21 sec/60 degrees at 4.8V
0.17 sec/60 degrees at 6.0V
Torque: 43 oz-in @ 4.8V
54 oz-in @ 6.0V
Weight: 1.5oz (42g)

S3004 ($12.99 at Tower)
Speed: 0.23 sec/60 degrees at 4.8V
0.19 sec/60 degrees at 6.0V
Torque: 44 oz-in (3.2 kg-cm) at 4.8V
57 oz-in (4.1 kg-cm) at 6.0V
Weight: 1.3 ounce (37.2 grams)

And then one you did not mention...

S3003 ($19.99 at Tower)
Speed: 0.23sec/60 deg @ 4.8V
0.16 sec/60 deg @ 6V.
Torque: 44 oz-in @ 4.8V
56.8 oz-in @ 6V
Weight: 1.3 oz (37.2g)

As you can see all these servos are nearly identical in performance. My LHS said that the S3151 servos would give a smother transition in movement but due to there frequent error checking They will use your RX battery up faster ( I have no idea how much faster.) For the money Go with the S3003's I imagine your flight pack came with 4 S3151 servos well Sell those on ebay to some tech junky and go buy 10 S3003 or S3004's so you are ready for the next plane after that.