I use 24" diamond disks and a 106" belt sander for my coldworking, so these tips apply to those machines. My favorite coldworking technique is all about avoiding the little bites, facets or scrapes you get when you put a piece down even a tiny bit off flat on a moving wheel. If the wheel is rougher than 320, you often get a little facet on the edge of the piece that you now have to fix. If you're on a 60-100 grit wheel, the little facets can be deep and a pain to fix, adding lots of time to coldworking because you have to grind past these bevels and move back up the grits again.
In my experience, if you never make these 'off-flat' mistakes, coldworking goes a ton quicker. So two ways I get back on the wheel that limit or eliminate this risk:
1. Stop the wheel - this sounds like it would add a lot of time to coldworking, but it's well worth it. I will bevel edges on a 400 belt while I wait for the wheel to slow a bit, then brake it by putting a wet sponge on the bottom of the spinning wheel. Putting your piece down on the stopped wheel eliminates the 'bite' for sure. I do this on 60 and 100 grit wheels since a mistake can be costly. (I don't bother with this for the first flattening since I'm removing a lot of material to start, just subsequent ones).
2. Set down in the center - When going back on a spinning wheel, put the piece back down very gently in the very center and make sure you're flat before sliding the piece to the outside of the wheel and applying pressure. This lessens the possibility of getting a bad facet from putting the piece down imperfectly on a fast-moving wheel. The center of the wheel spins a fraction of the speed (in swept area) as the edge, so any off-flat that happens when you set it down is less likely to damage your piece. This is why I would prefer zero diamonds in the very center of the wheel. The diamonds there are pretty useless anyway since they go slowly, so why not just have none, so you have a safe place to set your work back down on?
When I never get a little bevel or scrape my coldworking goes so fast. My process is to cut the sculpture punty off, flatten on 60, remove the 60 scratches on 100, remove the 100 scratches with belt on a 400, then hand lap with 400 grit. This results in a beautiful satin bottom. I can move through this in about 15 minutes per piece if I don't have to re-do any of the process.