Very similar set up to mine I think, Mick. Your 3x 22mm holes add an extra 10.34 sq cms of intake area, my extra 38mm hole adds 11.34 sq cms. Taking the original 38mm hole into account means you've about 5% less intake area than my airbox.
Before I did this, I'd calc'd the intake area that 3 others, some time back, had used with 115 mains (2 had used 40s, 1 used 42 pilots IIRC). I can't recall the figures, but there was a spread of areas in the region of 20% around my +1 x 38mm hole. It didn't seem too critical, & these 3 posters all reported good running throughout the rpm range. (Which is my situation too.) I think I've now set my (40s jets) pilot screws at 2 3/4 out, having tweaked a bit from starting ~ 2 1/4.
I have Dynojet Needles (from TBS Keihin kit) which are more aggressively tapered than stockers or Thruxtons, which I had tried before opening the airbox. I think the Dynojets work even better now than before, but for the bangs per buck, the Thruxtons would do quite well imo & be a worthwhile upgrade with a more open airbox. (I made no clip position changes to the DJs after adding the extra 38mm hole.)
Pop on decel from the Thunderbike 3-1 is now very much less from a sharp roll off after an aggressive squirt to 6 or 7k rpm or so. MPG (factoring out the Ignitech ignition) is down a little, maybe 4 or 5%. Considering that & the excellent accel from all revs, I'm thinking fuelling is fairly good & not planning any other changes.
Hope this helps, Mick?
Just while discussing more power...
The performance imo is now really showing up the chassis, especially, I think, the back end/ swing arm. Hard accel to the red line really seems to get things flexing & sqirming. I've had a couple of test rides out recently on a Suzuki RF600 sportbike I'm fixing/servicing for someone. It's about 100hp, doesn't feel much more powerful than mine (tho' a little) but there's no comparison with it's chassis - rock solid, over less than perfect roads, caning it to 120mph+. The RF is a tad lighter, shorter but only 41mm forks, so think the front end's about even. It's swing arm, however, is an aftermarket braced brick of a thing, just massive. No flex or squirm that I could feel, & I think that's why.
So, I suspect the Legend/Tbird swing arms are a major weakness (relatively). A bit too skinny & the axle mounting system no where near stiff enough. The T3 Trident/Sprint eccentric system looks like it effectively wraps a lot more swing arm metal around the axle ends. (Surely needed with 98hp on tap?) It's an important area in swing arm/wheel stiffness performance.
What do other folks with big power upgrades think?
Not sure what's involved, but a T3 swing arm might be a project next winter....
Quite enough of my ramblings for now
Mike