alright since no one else is going to say, i'll go ahead and say it.
GT - load the bar up with 280 and do it. you've been doing 275 for the past three months...it's time. i, just like you, fucked up my lower back about two years ago when i first started doing deads because i was increasing weight faster than my body could handle. i was going up 10 pounds each week and finally my lower back said, "NOPE!" it was too much too soon. i'm guessing this is most likely what happened in your situation. after taking time away from them to let the muscle heal, i got back into them. i increased the weight i was using much slower the second time around, allowing my body ample time to get used to the weight so i wouldn't come to the same unfortunate end that i did the first time around. two years later, i'm lifting about 70-80lbs past the weight at which my lower back went out. you've given yourself three months to get your lower back stronger and more capable of handling the deads. you just need to decide it's time and go for it. i guarantee you'll come out of it thinking, "well shit, what was i worried about?" then go up to 285 in a few of weeks if you feel comfortable.
reps on deads are terrific for building mass. yeah, no doubt it's not the best thing in the world for your spine, but neither are squats. no one on this board speaks negatively of reps on squats, in fact most people advocate high reps. all the "good deadlifters" are powerlifters, so of course they are not running around talking up sets of deads over 2-3 reps. it's not the way they train. if i remember correctly, gt is a bodybuilder. sets of deads in the 5-7 rep range will work well for his goals.