if you have magnetic plates to put on the dbs so you can go up in much smaller incriments, then it'd work. going up 5lbs per db every week, however, you'd probably plateau a lot faster than you wanted to. the weight increase is just too much.
5x5 will net you gains if you do it right. my flat bench max went up 35lbs in the past 3 1/2 months. i'm going to switch to incline bench 5x5 when i come off of this week and a half rest. i don't want my incline bench to lag too far behind my flat bench.
use dbs for your 2x8-10. or you can do what i've been doing. i do 3 sets, 10, 8, 5-6 reps, in that order. i increase the weight every set, and the weights i pick for each set are heavy enough that i just about hit fatigue on every set. i liked this better than doing 2 sets, and if i hit 6 reps on the 3rd set, most of the time i would bump the weight up on each set the following week or every other week.
quite a few people around here running 5x5. you'll get lots of good advice.