Using HS-425BB servos on the elevator halves on a pacific aeromodel Edge 540. One servo is moving at a greater arc and at greater speed than the other. Is this common?

Are you using a reversing "Y" cord?

change which servo is plugged into which connection (at the servo's lead ends this will reverse the elevator control... but we're just doing a test, flip no reversal switches.)

Now did the one with more travel become the other servo? If yes... the difference is not in the servos... its in the transmtter programming if doing computer mixing... or in the reversing Y if doing it that way.

I am using a Y cord

Has to be some difference in the mechanical connections then. The push-rods are not equidistant from servo shaft on the servo arm or not in the same holes on the control horn. Either way this will make for a bad day when you try to fly it.

Servos, espeically inexpensive ones like the 425 do, in fact, vary. They use inexpenseive motors and pots in there, resulting in slight speed and travel distances. So yes, what you are seeing is normal. (note, this isn't specific to Hitec, all inexpensive servos are like this)

To fix it, you need to do one of several things:

Ditch the Y harness and use two channels and mixing. Then you adjust the mix %'s so that the travel is the same on both sides. You can't really fix the speed this way, but if they are close, you won't notice it in the air.

or

Get a pile of servos and go though them until you find a couple that are "matched"

or

Spend a lot more money on higher quality servos, Hitec or other brand, it's not the brand, it's the price-point. But even the best servos to vary a little bit.

or

Get some Hitec digitals and a digital servo programmer, this allows you to set each servo's endpoints, travel speed, and a couple other parameters to match servos up.

or

Get a "match box" or equilivent. This is a box that goes between the RX and the servos that allows you to adjust the speed, center, and end points (maybe more) of sevos to match them up. These things were designed for the guys who gang multiple servos on to one control surface to get higher torque than they could get from one servo alone. With out this kind of matching, the servos will fight each other.

Oh, I forgot to add this one thing:

If the servos are pretty close, fly the plane and see if you actually notice it in the air. You may not. You might need to get someone who is a really hot acrobatic pilot (pattern or IMAC, not free-style or 3D though) to test fly it and see if it's worth fixing.

(the reason I say pattern or IMAC but not free-style/3D guys is that in pattern and IMAC, the planes are flown very smoothly and percisely. Any bad tendancies show up on their score cards, so these guys really KNOW how to trim a plane and they are really good at figuring how what is wrong with a plane in the air. Guys who just bore holes in the sky, or spend all their time hanging on the prop don't always have the experience to really fly the acrobatic routines smoothly and percisely. For them a 3D-only guy, a very slight roll coupling with elevator might not be a big deal, but for a guy who flys percision acrobatics, it would be huge.)