Sorry about the delayed response, dirt. Been out of town for a couple days.
I went with the 4" angle grinder discs. I just don't see where that extra inch is going to help that much.
Maybe it does, I don't know. That extra inch might help you keep the disc flat against the surface while using it?
And about $225 is what I paid for mine with one set of 8 discs.
So, the flat laps you see on eBay for under $100; I take it they are homemade rotating laps? And what kind of laps do you use and where do you get them.
I have a homemade 18" rotating flat lap. I use 12" silicon carbide peel-and-stick paper sanding discs on it and use every bit of the space the 12" allows.
If you get one, I would think about a larger one. One size fits all.
Yes, the vibratory laps take about as long as tumbling a stone.
That's why I was thinking about using them for the last few steps to polish.
And the learning curve to using them is as long as tumbling. Those pans have to be level and not "dished" in the middle from previous use, if you get a used one.