I run a 12 Y.O. MTB frame that was designed for 50mm travel forks. 80mm is out of the question for this frame. Even the 63mm of my current fork, plus the increased tire clearance make the handling noticably slow. That said, I feel the short travel of this fork offers some advantage over the 80 and 100 mm forks. On climbs the bike is noticably quicker, and there is less dive when braking. I'm quite happy with it-only on fast downhills do I miss the extra travel.
I'd suggest try it with 80, and if you like it, keep it. If not, think about swapping it for the 63. 17mm isn't that much, but you will notice a difference in your bike's handling.