For my 200g FO, I use 4tubes x 60inch regular T5's (not High Output). I only switch on the lights for 4-5hrs when i come home from work at night, and only when i want to look at the fish. During the daytime, natural sunlight in my living room is enough to let the fish know that it's daytime. Fish don't need lights, so I keep them off to conserve electricity.
If you'll be hanging the lights from the ceiling, then you won't have to worry about waterproof lights and you can almost go for cheapo T8 shop lights with reflectors.
Since you have such long tank, you can consider getting 2 sets of 48 inch x 4tubes. This way, lights will span almost the full length of the tank so you won't have dark spots.
My number 1 suggestion for FO's/Fowlr's wrt lighting is to not buy MH's or T5HO's as they're more expensive to buy, replace, operating cost is higher and they produce more heat.
Was thinking of going with 2 48 inch fixtures. Would like to keep my squamosa clam if possible. Sunlight supply makes a 48 inch fixture with 8 54 watt bulbs. I think this would be enough light for the clam if I put him up about half way. I've had him for a few years now and would like to keep him if possible.
you should be fine with two 48 inch ho t5 fixtures. i have one 48 over my 60 inch tank and the light spread is great. clams, sps, and pretty much anything i want grows under the t5's just dont wast your money on to many actinic bulbs they dont put out much par. oh mine is the 6 bulb so two 8 bulb fixtures will be great.