RE: DX7 Binding Problem
Both Rx and Tx have programs (firmware) that control the device's behavior. Some are faster than others. I have a DX7 Tx with a selection of AR6200 and AR7000 Rx. Some bound quickly. Some bound slowly. The Rx had different firmware "releases" - some old, some new. You can't tell by looking at the Rx. I sent mine back to the service organization (Horizon Hobby) and they upgraded the firmware on all of my Rx for free. They now all bind with similar speed.
Em, just re-read your post. You have two different products trying to work together (Futaba & Hobby King) to provide the same functionality that is normally done by a single piece of electronic hardware - one set of program code. I'll take a wild guess that the guys/gals that developed the program code for Futaba couldn't care less about the program code developed by Hobby King - it wasn't in their "program specification" - it doesn't surprise me that there would be / could be a "hand-shake" timing issue between these two products during the bind sequence.
Is your slow bind and issue? Probably not because it is a one-time event for each flight. If there is the similar "performance difference" during flight - you bet there is a potential problem. It would suggest that the servos would be lagging behind your input. How much behind? Probably not bad otherwise you would already have seen a problem.
Yea, I'm rambling - HTH