Not the same cabs, but I'm running two 350w 112s (Bergs) with a Streamliner 900, and I have the Bass at about 9 o'clock on the dial - partly for the sound, but also because, like you, I'm just a little wary still of cranking too many deep lows through them. I'm sure I'm worrying unnecessarily, I just need to do a few more gigs with them to relax... The Streamliner has a High Pass Filter, too, so the ultra-lows get, erm, filtered out, but even so, I fret a bit. I do hit the thing quite hard sometimes, I'm a pretty dynamic* mostly-pick player...
* AKA 'Ham-fisted, gets carried away'...