Put a mild brushless sytstem in the Roost and the diffs may be ok. A low kv brushless motor is not the best either because it can be too torquey which is also bad on drivetrain parts. Stick a Tacon finned 2030 brushless motor in it pair it up with a Hobbywing 18a esc stick to pavement and go have some fun. I run a 1/18 Ruckus with a 6200kv finned Tacon 2030 motor, 18a esc on 2s, with smaller tires and the diffs have been holding up. I tried a 2040 3800kv motor in it and tore a diif up so I went with the 2030 6200kv. A 2030 brushless motor is easier on the diffs. I have given up on the ruckus its just not as fun to drive as my other minis.
I have some Dromidas they are great minis in my opinion. They are highly upgradeable except the diffs but the diffs hold up pretty well to brushless even though they are plasitc.