On my 14 X 22 Cat, rowing from the NRS seatbar, my 9 ft. oars worked great. Then I switched to a 14 X 24 Cat, and started rowing from a AAA flip seat bracket over a dry box. Then they felt too short. I got 9.5 ft. oars and the length was right, but like slamkal, the 8 in. towers were too short to get the right balance (1/3, 2/3) on the longer oars. Now I have AAA towers, so I can tilt them outboard a little and still have a good height. Perfection !!!!!
The moral of this story for me is to quit tweaking my set-up
Good oars are expensive. I'd advise borrowing some different lengths from someone to try out first before laying out a bunch of money, then regretting your purchase.