I went 1.6 to 4, it hurt, but meh.
Yeah, the smaller the increase the less it hurts and the less you have to wait before another stretch.
I'd got 1.6 to 3, to 4, to 6 personally.
Another tip, say if you buy a plug or a tunnel, to save money on another claw, wrap sellotape around it to make it bigger.
I went
1.6--4--5--6--tape--8--tape--10
1mm stretches don't hurt at all and can just be pushed in. I left mine to heal until I could play with it loads, take it in and out etc without it hurting, then a few days more.
I reckon it'll take a couple of months using my unorthodox methods.