An interesting solution may be the ACK turboboard with PPC and graphics onboard for the Amiga 1200. Said to be released this quarter, but haven't heard anything about the price yet. Maybe someone know more about this one?
Another intersting solution could be the Dragon, if the Amiga 1200 is housed in a tower. Dragon offers a 266 MHz Coldfire and AGP so that a cheap graphicsboard can be fitted. The price of 350 Euro may be a bit costly but will probably give a nice performance. However this turboboard too is not yet released, but should be in the end of the month.
Otherwise if your monitor works with 800x600 this is quite nice too, does somebody knows if flickerfixers works with this resolution? Quite flickering otherwise.