[Papasmurf]

I was never a big bencher, i always used dumb bells before about 4 weeks ago. I picked up what i guess you would call a power lifting bench press form, where my rear delts and ass make contact with the bench, and i bring the bar to my top abdominal. When i first practiced and got this form down, it shot my bench from about 200 to 245, so naturally i was impressed. However, im beginning to notice a dull pain in my lower back, presumably because to get my shoulders rolled back onto the bench, i have a significant arch in my back. Has anyone else had this problem? Is it just maybe that my lower back is too weak to support the sudden jump in weight? or should i just concentrate less on arching my back, and maybe just holding it more solid?