If you have a widescreen, try 720x480. I am surprised a widescreen performs well at 800x600, though.
You should be able to pick up a SB Live w/ EAX for $30 which isn't a bad card, but isnt the best either. Nothing above that will give you better performance on an emulator though, and I dont think EAX will help in an emulator either

I use a SB Audigy 2 ZS Platinum for gaming, movies, and recording. Awesome card, just expensive. The front drive is convenient but not 100% necessary.