The two rifles you first mention would be fine for F-Class, and when I was in Houston, I know shooters that used both out to 1,000 yards with good sucess. If you are talking anything other that .223 REm. or .308 Winchester (shot from a front bipod), then the weight maximum (not including front rest or rear bag) is just a touch above 22 lbs. The .284 is a quickly growing caliber of choice, as are all of the 7mm magnums (SAUM, 7/300, 7WSM, 280, 280 Improved) and the 300 WSM. They give a significant benefit in the wind, but extract a price when it comes to recoil. My brother shoots the .284 Winchester and loves it. I have and shoot a true 7WSM (for 3 barrels and roughly 5 years now), but may switch over to a 7/300 WSM or down to a 7 SAUM when this next barrel is consumed.
Barrel length and contour are more tied to target velocity and weight. If you build a standard rifle, you'll have something on the order of 30-32" long barrel, in a tree trunk looking contour. Mine is 30 inches, 1.250" for 5 inches then tapers to 1.00 at muzle." Nota lot of taper on that beast. BUt when you have 22 lbd to play with you can make the barrel big and heavy. If you go straight .284, get a 30-32" barrel, you'll want to be in teh 2,800+ fps node. and its easier to hit year round with a long tube.
The NRA rules are a decent starting point, but so it going to a local match ans simply seeing what people are using on the line and how they are doing it. IN some cases, you'll not see much in the form of advertising about F-Class, since its a subset of High Power.
In my local Area, Las Vegas, we are combined for nearly all matches (except we run a separate 600 - mid range match) monthly at my club.
good luck
JeffVN