Thanks, Derek! I'll have to read through your bench build. It's different than my basic design, but I'm sure I'll find many helpful tidbits in those pages.
A little bit of searching later and it sounds like a 3-4" gap in a split top is pretty good. Since my bench will be in the middle of the room, I'm not too worried about depth. So, I could go with a symmetrical split. Maybe a pair of 10-11" slabs, 3-4" thick, with a 4" gap in the middle for clamping. I'd also likely make a small sliding tool tray that can sit in that gap to hold a few items while I'm working, but still slide out of my way when I need to clamp something.