Now that I've had my chance to be a jacka-s, I'll actually give you a worthwhile answer.
Section 13 of the manual covers painting (at least in the RV-7 manual). A paragraph from that states the following:
"The question of whether a painted or bare aluminum airplane goes faster is often raised. Experience with the prototype RVs has not provided a definitive answer, so it would appear that there is little difference in skin friction drag from a typical painted surface to a typical bare aluminum surface."
Ultimately it is a tradeoff from the increased induced drag due to the paint weight, compared to the increased skin friction/parasitic due to a better surface finish (assuming you can paint well). Given that we are running non laminar flow sections, that surface finish may not be so critical.
I think realistically it comes down to other factors, such as... do you mind the glare off the topside of the wings, do you like polishing aluminium on your weekends, do you mind the extra 15-25lbs in paint weight and it's CoG impact (especially on a -7), do you want the best corrosion protection, do you have the right conditions/facilities/$$$ to paint, and what do you want your aircraft to look like? I spent many months sitting on the fence on this one, but I have taken everything into account and decided to paint with a single pack valspar (Wattyl) zinc phosphate epoxy etch primer with a Valspar (Wattyl Colurthane) polyurethane top coat. As a datapoint for Australians out there considering using Colourthane, it turns out that the head office in Sydney will colour match what ever colour you want so long as you send them an sample chip they can match to. I wanted a Federal Standard 595 colour, so I ordered a chip from the States and they will match it free of charge.
Tom.
PS. if you decide not to paint, here's my favourite "no paint" paint job (C-GSMC). It's polished so it's light, but it's also red, so it goes fast!
Does paint really make a plane faster?
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