For distance racing, the F20C would be the ticket, ignoring cost.

I'm going the F18 route, settled on that a while ago, just working on the means. The N20 and F16 MIGHT be faster round the buoy course on light air sailing days in the Chesapeake, but that has yet to be fully proven as its been a long time since a competitive F18 has sailed with the fleet. A few other reasons to go F18 IMO:

1) Much larger nationwide fleet. Need a big fleet to grow sailing skills.
2) Original short-board boats will work fine on the Chesapeake. Breaking a F20C board while short gybing up the Eastern Shore doesn't sound appealing.
3) Large used market
4) Not tied to one manufacturer, one sail builder etc. Maybe lower overall running costs and slightly better quality (the F20C is a well built boat with great rig so not a big factor here).
5) The boats are competitive around a distance course, even if you are heavier, although not ideal.

For me, it comes down to options, and the F18 has the most options. If your #1 motivation is a straight line honors machine and cost isn't a concern, F20c or SeaCart 30.