Go with the 285th. It is only 5% larger, while the 350 is 17% too small
For those of you who slept through high school math:
(300 - 285) / 300 := 0.05 (large)
or
(300 - 350) / 300 := -0.1667 (small)
The choice is up to you. As a matter of personal choice, I do not mix scales differences in excess of 10%. The difference can be visually jarring. Even then, something which is 10% large may just appear wrong. I tried to put 1:144 scale Oerlikons on a 1:160 scale PC and they just didn't look right.