I think the 60 is a great option for a full size gig, anything larger will also work, but for a species tank you don't need to go bigger IMO.
I have a few pieces of sps around the edges now as it seems to have slowed in growth, I fed every day at first and now only feed once a week if that.
Smaller tanks are doable but I would not really want to go smaller with a full size gig.
The tank has>>>
corner overflow
eheim 5000 compact+ return pump
an octo extreme 160 skimmer
a grotech dosing system
a 1/4 hp chiller and eheim compact 2000 feed pump.
two vortech mpw-40
a tunze osmolator
a tlf phosban reactor with GAC
a lumenmax reflector
a coralvue 400watt non dimmable ballast
a reeflux 20000k bulb, just switched from 12k.
liverock, sand (caribsea), a pair of percs, a blue spotangel, two dispar anthias, a possum wrasse and an orchid dottyback.
a skunk cleaner, two perciclemes anemone shrimps, snails, annoying furry crabs, one blue knuckle hermit crab (five years old) and various sps corals.