Drew: If you are using stress-graded timbers, then a nominal 5x7 piece would be graded as "posts and timbers." The bending strength of Red Oak posts and timbers varies from 575 to 1250 psi, depending on the grade of the material. Assuming worst case, these joists will only support about 110 lb/ft, which corresponds to a distributed load of only 43 psf on the floor. Normally, a home is designed for a floor live load of 40 psf. Your floor system itself will probably add another 10 psf or so (including the joists, floor sheathing, and finishes). So technically, the joists would be inadequate for strength. However, they should be ok for deflections. You need to be sure that you are using at least #1 grade Red Oak timbers to avoid this problem. I don't have separate bending strength data for bur oak (a subspecies of white oak), but the strength vales for the white oak group are only slight above those for red oak.

Dovetail connections might lead to problems with the carrying members. If you dovetail your joists into wall plates or summer beams, then the plates or beams might suffer distress due to the notch effects.