TF-89 is more powerful than the B26. Mine shoots in the high 700's,,,, around 780 and mine isn't broken in quite yet. It's a real powerhouse for sure. I find mine to be a bit hold sensitive, but I seem to be the only one who has this problem as the other members who have it haven't complained of this. My accuracy with the gun is very good, provided I'm shooting offhand. If I shoot from a shooting bench, with the rifle resting on a support, then my groups open up. I can't figure it out, but it's ok cause I use the gun for hunting and when I'm hunting I'm certainly not sitting at a shooting bench :) The 89 is a nice looking gun, relatively light and really packs a whallop. I like mine, although I'm still refining my shooting techniques with it.
As for the B-26,,,,,, should shoot in the 600-700 FPS range depending on pellet choice, is a nice solid shooter out of the box, is very accurate, cocks nicely and has a very good trigger. I have 2 of the B26-2's (thumb hole version) one in .177 and one in .22,,,, can't say enough about them,,, great rifles !! I use them both for pests and small game and they perform flawlessly.
If I could only buy one of them I'd choose the B26.
Jeff