For my Bf-109 series, its 200 for Machine guns, and 150 for cannons. I rarely fire anything father out than that, other than to posibally make them turn. My 190's its 300 for Machine Guns, and 200 for the cannons.
When attacking bombers, I always attack head on if possible. If there isnt any fighter escort around, i Take my time in attacking head on. No need to rush it. But if fighter escorts are snooping around, then I will rush it a little, but I try not to make dead on 6 o clock attacks, just 2 dangerous.