my ae82 has ac - and it doesnt kill it too much - just not the most economical beat - drop a tank of fuel from around 550km to 450km
but maybe mine doesnt kill it too much cause i have the 1.6l engine and still only have the 4sp box in it - maybe it would hurt more in 5th.
but i reckon pu a 4AC engine in and fit the factory air it came with.
BTW factory air really isnt fatory air on these - it was all fitted by the dealers as an add on