our car has custom mounts made up. custom makes them sound fancy but they are not. tho original runners were chopped off the seats and welded to a box section subframe to which the seat then bolts.
it is steel and could be lighter but just be aware, that is all that holds the set in in the event of a crash.
as above, in theory lower seat equally lower centre of gravity and you will go aster but i doubt you will notice any difference. might feel faster though!! you wont be fast if you are not comfortable though. have a sit in as many bucketted cars as you can and have a measure up. are you off to the pod at the weekend? if so i'll pm you my number and you can have a sit in der panza.
just a quick thought, if you liik at rally and touring cars, their seats dont seem particularly low. at a pro level, i think there's a bit of science goes into seating positions