Your biggest concern with dragging on inclines, is going to be the overall length of the unit. Shorter is better in that regard. All other things being equal, fivers will have more clearance. The fivers people buy tend to be longer units. But comparing a 28' TT versus a 28' fiver, just as an example, the fiver will have less overhang behind the axles, and will be shorter overall because of the portion over the truck bed.
Another thing to look at is the location of the waste tank drain. I've seen some that were perilously close to dragging. Since we like to get off the hard pavement a lot, I paid close attention to that when shopping. My preference is for the waste drain to be very close to the axles. If you draw an imaginary line between a tire and a drag point on the bumper, you don't want the waste drain to be below that line.
Based on your description of the RC field, I don't think that will be a factor either way.