That is the exact reason they made the 6/750 motherlode.I have 8' too and the gavita 1ks had to be dialed way back all the time but i didnt know any better at the time i bought them.From gavitas facebook page,
''The Gavita Pro 750W DE EL lamp for our Pro 6/750 DE FLEX fixture. It is a unique lamp in its class, the first 750W electronic HPS lamp to hit the 1500 micromol level. Many climate rooms do not have the height you need for 1000W lamps, or the crop is too high. A 750W lamp works much more efficient in the 600-825W range than a dimmed 1000W lamp.''
Just about the time we figure it out the new latest and greatest something else will come along,Im already jonesing for CMH's to play with after seeing growers here use them,lol.