use 40 pitch, then you can get motorcycle chain in 420 or 425(one or the other, can't remember), there are tons of charts with link size comparisons, being able to get good O-ring chains will increase the life and lower stretch, which will pay off when you aren't dealing with issues. I went with 40 because I could get it and its cheap form is better than what I could walk in and get locally in 35, but I live in the sticks. so that may be different for you. my vehicle with a heavy driver runs 750ish lbs, and thats on the light side IMO cheapo 40 has held up well enough, I buy it for mockup cause at $16 for 10ft, I can change things and not cry about getting more chain
if you can, try and get motorcycle style sprockets (so the 420/425 (not sure which) that work for 40) as they are the same pitch and dimensions, but the teeth are longer, so less chain issues usually.
I BELIEVE its 420, about 80%, but there are enough searches you can do on the net to answer that. I would like to warn you to try and avoid half links though, in any size chain they are not designed well from what I've seen. if your vehicle is lighter, your mileage may vary, but they don't work for me.
P.s.> well I was 80% wrong, its 425 that is the same according to
http://www.gizmology.net/sprockets.htm