mparker's point about the slurry is a good one. Back when I was using sandpaper for all my lapping, I did the 4K side first. That smoothed out the paper and left a 4K slurry on it, which put a nicer polish on the 8K side.

I think the concerns about grit contamination are a little over-emphasized. I've done a LOT of lapping: probably lapped my three different Norton stones for hours if you'd total it all up. (I hone a lot of razors, and my first Norton was defective, which led me to several marathon lapping efforts.)

And I can't say I've ever had grit get stuck in my hone. Not saying it doesn't happen, but if you use good wet-dry sandpaper like Norton or 3M, I don't think it's that common.

Josh