It's G. winemilleri. It's not G. brachubranchus because they have a spotted caudal fin while the one in the photo is striped. Not dicrozoster cuz the body shape is wrong and I dont see any evidence of the Y bar. G. proximus has a larger lateral spot. Thus of the common species with black throats we are only left with G. winemilleri.....I could be mistaken though cuz I'm still waking up.
For a 75g definitely stay with the smaller species like orange heads or pindare