Hey Old Goat,
Are you using 2-bulb 4 footers on your 7 fixtures? I'm thinking of using 8, 4-bulb 8 footers in two parallel rows for a total of about 46,000 lumens (2900 per bulb x 16)
I have a 23 x 23 sheet rocked and painted white garage with a 9' to 14' sloped ceiling - and no obstructions...