When I was ca. 110 kg I didn't rate my 92l Evo 2004 at all because with the small 24 cm it came with it was very hard to get it moving. This all changed when I put in a 25 cm Drake Natural Wave because the board got heaps more drive, but didn't lose its appeal as a wave board. Since that time I've lost about 17 kg and played around with all sorts of fins. The Drake 25 cm stands out in terms of drive/looseness. With a 5.8m2 sail I can get this combo going in pretty light winds nowadays (ca. 13-20 knots maybe), and even if the wind drops to bugger all I still get back in no probs. When the wind and waves pick up a bit I tend to go down to a MFC 22cm so that the cutback doesn't feel over finned. Makes the board looser too, and in heavier winds you don't need so much drive.
Try the Drake 25 cm. If you're sailing in waves I'd be hesitant about going up to a 28 cm crossover fin because you'll probably straighten all the fun out of the board.