Hmm, I've never researched it myself but I assume there's a different resistance in the 96W bulbs that the 65W ballasts aren't configured to run with. probably bad for the ballast.
What's the intent? You won't get more performance out of a 65W ballast with a larger bulb, as the ballast will only put out what it can - assuming it lights up. Why not use the correct bulb? If you want more light, you need to upgrade the ballast too.
In the DC Metro Area? Check out GWAPA