I bought a 40 tooth rear sprocket to fit my 04 749S.
This was a daft move as you need a longer than standard chain with that size of sprocket. The slots in the swing arm arent quite long enough to accomodate the larger circumference of the sprocket.
Ive since fitted a 39 tooth gold alloy renthal and this will slightly lower the gearing (which hopefully make it a bit easier round town) and I didnt need to change the chain. Fitting a lrger rear sprocket lowers the gearing which reduces top speed but gives better acceleration.
Looks trick and is considerably lighter than the standard item.