On my car with MS/Eibach 30mm lowering springs, I fitted
Yellow dot roll bars front & rear. Reduced body roll further, sharper
initial response. Felt to make a big improvement on track, response seemed
better entering corner, less roll & more grip mid corner, but did feel to have a bias toward power on understeer at all speeds.

Orange rear roll bar then fitted with Yellow front
roll bar. When pushing hard on road, back end feels a little looser. On track, balance was much better (less understeer) & more fun.

Comments on above set up from a friend who drives a
Mk3 sport with stock suspension: Surprised how little ride is compromised (the
Mrs noticed though). Body roll reduced, but not fully eliminated. Low speed
understeer on road, seems to need to carry some speed into corners to get some weight transfer for it to bite. More tail happy at higher speed cornering.

On various forums, people have suggested Red front
& Yellow rear roll bars give good balance. These can both be picked up on
Ebay quite cheap from scrapped RX8s. That set up should be similar in terms of
balance (just a bit softer overall) to the Yellow front & Orange rear that
I like. If you don’t mind buying new bits, the MS/Eibach adjustable roll set
would seem a good option, as that is similar to above (yellow front, orange rear), but with some easy adjustability.

Fitting: RX8 bars fit MX5 mk3 with no mods & don’t
foul anything. Drop links are a sod to get undone if rusty, mine were ground
off & 4 new ones fitted! Rear roll bar is a doddle to change. Front
required the radiator to be unfixed & lifted a few inches (coolant hoses
not disconnected though), to allow radiator to be raised enough to get the roll bar out & in.