I contacted Ricksmotorsportelectrics.com and while they don't have an uprated stator, they say if I use their hot-shot plug and play Mosfet rectifier/regulater, I'll get an additional 40 watts of power. Click Here to see it.
The other thing I've been wondering... I wonder if someone who sells parts has a stock 690 stator and a stock 990 stator on hand to eyeball them side by side and see if they're the same size. I took a look at the parts fiche but that's just a drawing. They've got the same plug on them. If they were interchangeable that'd be awesome, wouldn't it?