When I first starting using weighted dips, I saw i was able to add 2.5lbs a week. There should be a large capacity for you so I wouldn't expect you having an issue, especially since your bench numbers are good.
As an example, I have now surpassed the total weight I use for dips than I bench( dips 107.5 + bw 160 = 267.5 for 3 x 5, bench @ 260 1rm) I suspect though that gains will become more difficult as I approach higher % of bw.