The 4200rpm drive isn't a HUGE issue, imo. I've only used the 933mhz iBook extensively, but I find even that to more than adequate for daily use. The areas that you will notice the biggest performance hit is launching applications and if you are doing something that is using lots of virtual memory. If you find it to be a problem, get the base HD in the iBook and replace it with your own 3rd party 5400rpm drive. You'll get better performance but less battery life.
The video output from the iBook I have used was pretty good with the hack. You can up the resolution to be more than th ebuilt in LCD with the hack as well, which makes it look much better for those big displays. I'm not sure how much quality loss you will have going to a DVI LCD input from the iBooks VGA output... I plugged it into a VGA LCD and it looks fine to me, but I am not a professional artist or designer type, so take that with a grain of salt.
If the video out is a big deal to you, I would wait untill MWSF and see what the PBs look like at that point and then make your choice.
Regards,
Rob