whilst it wasn't a playtest, I did sit in our Cthulhu RPG last night bored enough to roll over 50 lots of hunter dice, eg 5 beam dice using TBS.
I didn't record all the rolls however, I had 2 of 8, 4 or so of 7, 1 complete miss, 2 of 1, 1 of 2, then everything else was 3, 4, 5, 6 with 5 and 6 seeming to top the charts easily enough. even on the all 5 hit with re-rolls, I then went and got only 3 more hits.
It made it all more predictable. The GM when he realised what i was doing rolled a few Sharlin beams, getting 9 hits as an average.
so no complete runaway beams, but then only one complete failure as well. personally, I think the system which seems to guarantee more or less 3 hits minimum with a 5 dice weapon, and caps at 8 is something your opponent can understand, and means that tactics will become important. as you think you will send your Warlock in to cover the remaining fleet, knowing it should take xish damage rather than sending in a warlock then seeing a 25 dice beam hit from a 3 dice weapon!!
will of course be actually playtesting this next time, but just though that i would let you know my rolling practice results ;-)