I have the Ultra 9 and Ultra 5 and a 30CB9 (the 9" prior to the Ultra). That little Ultra 5 has most certainly earned it's spot.
My advice for TB Ultra .30s is this: either buy both the Ultra 9 for real suppression and the Ultra 5 for handiness, or buy the Ultra7 and have the best of both worlds. I have significant experience with all 3 of these and I can tell you that the difference between the sound of the 9 and 7 isn't much, 7 to 5 however is quite a bit louder.
That's good advice (and basically what I did) and IME it seems that the jump from 5" to 7" is the largest increase in performance across the entire spectrum.
If 2" more isn't an issue, I'd get the 7. If you plan on getting two, get the 9 and 5. If suppression isn't key and moderation is, the 5" will make it happen. I get what you mean about performance. If I need true suppression, I haul out the integral .22 with built in 12" suppressor. It's not much louder than this keyboard is right now!
My 5" will take supersonic .300BLK from an 8" bbl. down to manageable levels. It barks still but the bite is gone? Won't hurt ears. With larger rifles earplugs may be ideal. I sometimes use earpro with 'em. But I can generally fire the 5" without earpro and not suffer. Works great on a 6.5G SBR I have too.
Also, as far as I know, the TBAC Ultra 5 is the only moderator length can that actually tests as a no-shit suppressor. It's a great choice, but it's not my first and only choice if that means anything. If I only had one it's be the 7 for sure.
Also, regarding length, your mount will be a little over an inch, so with the can on it only adds 4" for the 5 or 6" for the 7 or 8" for the 9. The 5 is as close to having nothing on the end of the barrel as you can get, while still reaping some of the benefits of a can. It's light years better than just a brake. The 9" makes my 6.5G sound quieter than .22, just the sonic crack.
Good luck, you can't go wrong with these guys.