2'9 is what I used to do with one of my old geldings. Haven't jumped in over 4 years now tho(due to injury). Haven't ridden much even on flat for that matter. I have jumped a couple 3 foot fences on multiple occasions tho it won't count because they were speratic occasions.
When I had time to ride every week, I jumped up to 2' on accident as my horse jumped the blocks, instead of the pole which was at 1'. :lol: But I haven't jumped in 2 years as I took a break from English after a bad fall, and am now just riding Western/English for pleasure and goofing around with speed events(not competing).
The biggest course 3'9" but I jumped my horse 4'a couple of times when he was a sale horse. He is probably maxed out at 4' though he is much better fitness now it might be time to try and see where he is actually maxed out at.