Almost time for the machinist!

Its almost that time I'm getting excited as my project progresses. I have never took anything to a machine shop or had any work done before I have talked to the machinist a couple times and he has been very helpful I have a couple of questions I don't want to keep bothering him lol.
1) does the cleaning process remove paint? Do I need to remove all the paint before I take it to him?
2) this is the biggie. Me and the machinist talked some about the overbore and I told him I wanted to go enough to get it cleaned up. I want to go at least .030 because the piston weight for the .030 is almost Identical to the original pistons but .040 is only like 2 grams heavier. Here is the question. Is there any performance gained from a .010 overbore? I think it adds about 2 cubic inches or so and maybe a touch of scr. But is there gonna be a noticeable amount of gains between .030 and .040?
The reason I ask is I was gonna just wait and see if. 30 would be enough and if it is go with that. But I'm kinda thinking about just telling him to go .040 and be done with it so I can order my pistons and get a head start on fitting them to the rods while he has my block. I'm afraid if I order the. 030 piston and it's not enough to clean it then I just wasted time and money. I'm almost positive. 040 would be enough tho. Or would it be best to just wait and let him make the decision between. 030 and .040? Thanks guys/gals.