One suggestion I’d make is trying a mini band stretched around the back while db benching. I haven’t actually done this yet, but I plan on picking one up from elitefts.com soon as I use only dbs for benching (haven’t bb benched in a few years).
I think the advantage of the mini band is that it will allow you to address one of the disadvantages of the dbs in that you start in the stretched position–the band will make the resistance lower at the bottom and higher at the top, thus minimizing that issue. Also, it will allow you to use a lower weight in the db, which can be an issue if you’re working out somewhere that isn’t “hardcore.” Another advantage is that it will give you a variation on the movement, and that is always a good thing… now if I can just figure out how to attach chains to dbs.
I wouldn’t use the band all the time, but it would be good to mix it up, and for ten bucks you can’t go wrong.
On the db to bb ratio, I think it’s a personal thing, but once you figure out what your ratio is, it will be consistent for yourself. For me, 110x5 with dbs was ~305x1 with the bb (haven’t bb benched in awhile so I don’t know what it is now).