I've never noticed a DR difference between the 100/Rage and 200 chips. I didn't even know there was one (or forgot*). I use both 7500s and 9600s, and see no difference.
Your 8500 is fine. Not really any different from the 7500.
All this talk of 8/10/12 bits is fun theory, but understand VHS is like 6-bit dithered. So all the extra bits become moot.
AGP AIW cards are currently still cheap, under $50. I consider $50 to be gambling money, so feel free to buy and see for yourself. But most likely you're just having a "grass is greener" moment.
* Apparently forgot was accurate. We discuss this every handful of years.
The last time was here: http://www.digitalfaq.com/forum/vide...-original.html
Several more if you search the forum.
Why did I forget this? It's just trivia. Nothing that affects usage. 9-bit vs 12-bit means nothing when the consumer sources aren't even 8-bit.