I'd start with 19 40 its a good comprimise between track speed and belt life. I've seen and heard of a lot of 174's eating belts this year geared 20 40 or higher, they just have soooo much traction that a bit of gear helps the belt life a lot. I wouldn't worry too much about the chain at 18 40 but I would change it more regularily for sure but 18 is probably too low for you anyways. We had a $hit show with a snapped chain last weekend on a 19 40 162 sled but the chain was miled out IMO. 1500-2000 km on your chain depending on how you drive max. Cheap insurance.
M5