Yeah, I bowl on a shot like that every week.  It really does hurt your mechanics when you don't have to focus as much, it makes you relax too much.  Anything between 4 and 12 for us will hit the hole, depending on your style, medium to high speed with medium revs is the best, especially for the guys that can get the ball to slide the first 30 feet before it starts revving.  Including a average sized tournament, there were 7 300's shot at this house last week, and only 3 were in the tournament (one of them being shot by a buddy of mine!).  There's only been one 800 at this house so far this year, but new pins, new kickbacks, and a new pindeck are all contributing to solid back row leaves and a lot of off spots.  Carry is the only issue, hitting the pocket is not.  Only thing I might offer would be if you make a "bad" shot, turn around as quickly as possible, don't even watch the ball roll down the lane, just ask someone what you left, if anything.  That doesn't help a lot, but it also doesn't allow you to see how your miss reacted, in essence leaving some doubt about whether or not that kind of miss again will result in a pocket shot.
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The weekly signature series, by Hamster.

I was bowling one of the higher average scratch bowlers in league a month or so ago who bowls with average speed and maybe 5 revs from 1st arrow.  On one shot, he left a 9 pin.  Walking back, he frowned and said, "Nobody that throws a fag ball should leave that pin."