Personally i think your situation reflects the dissatisfaction about the assault resolution in EA (ie. hack-down can get skewed horribly on one roll) i brought up in a thread in the EA forum a few months ago (as mentioned by Ulric). Ironically since those three horrible games where we got 4 or 5 ridiculous results (for and against) i haven't seen anything so crazy since. On reflection, i think the simplest solution is simply to average the 2D6 result instead of choosing the best - this still provides the risk factor but mitigates it further.
At the time my play-group discussed getting rid of some of the randomness generally. We mentioned using cards - i think Parintachin's method is as good as any i have seen, though could also be played without holding a deck, or at least a smaller deck.
We also thought about introducing a number of player re-rolls like blood bowl for those horrible results which screw your turn (i have a personal habit of missing 2+ activation's ( i've managed 7 out of 10 in first turn 2 games in a row.) Another friend is notorious for never missing a saving throw - annoying when he also plays "RA spam" nids too.
More radically I also thought about automatically going with the average result when rolling 6 or more dice (useful in the bucket of dice GW games) - divide the number of dice rolled by 6, and only roll for the remainder - ie. 16 dice at a 4+ would give 6 successes automatically and you roll for the last 4... Though to be honest the big rolls seem to throw up "unfair" results less regularly.
But to be honest, in the end i we all sat down and had a chat after a game and realised that at least in our group it was actually our attitude change which was sucking some of the fun out for us. We realised we had been all playing super competitively (mainly trying to get nids to work ) swapping and refining lists, rereading rules, tactics articles, bearding ideas, pre-measuring every follow up move etc, etc. I guess we were trying to go for the "chess like" competition. In the end we all agreed it would be more fun just to go with the flow again. The only change we made is to ban pre-measuring, but otherwise we have all just chilled a lot and it has been much more fun since (though this may be cos my my rolling has also been damn lucky since
