I'm no expert, but will relate what I experienced & plan to do, YMMV.......
2011 Season I made 176 passes, the rings were OK but I replaced them anyway, the heads got a clean up & light porting, I installed new MAP Sensor & Injectors, and finished the must do mechanical fixes to the tranny (V&H 2nd gear), had already done the clutch basket. Also changed the Secondary cam chains for good measure. Bearings are a must do once the case is split.
2012 Season I made 76 passes, I do not plan to pull the engine at all, I will be changing the Throttle Body, as I am concerned about the cross shafts breaking, the unit I have has been erratic with idle stability.
2013 Season I anticipate making at least 45 passes in a New England only race season, I'm not sure how many AHDRA races I'll make, but each event I make as many as 20 passes in a Friday to Sunday time frame. By the end of 2013 I will probably be at the point where I will pull it, might change the rods, rings and freshen the heads including valve guides. Inspect the tranny, might do an under cut
2012 was my first year, bought the Destroyer in November, 2011. Prior owner said they had 34 passes on it since new. I had about 180 Racepak files downloaded, and I know I missed several. I would estimate I had at least 200 passes since buying it. That means at least 230, maybe as many as 250.
Interestingly, my quickest time was the last event of the year and I thought it might have been getting tired - an assumption based only on the number of passes on the engine.
Upon tear-down, Lou remarked the engine really looked good, the only problem being worn valve guides. In prior conversations with Lou, he mentioned having seen Destroyers with as many as 250 passes. That's probably the outer limit, or at least getting close.
pulled the motor down to freshen up with 140 odd passes, valve springs were well shot and an inlet cam was picking up a bucket, pistons ok, replaced rings and gave light hone, replaced shift forks and shafts as preventative measure, and installed v&h second gear, replaced big end and main brgs and rod bolts. picked up 7hp form before and after.
Best 60 ft = 1.358
Best 330 = 3.813
Best 1/8th = 5.911
Best ET = 9.461
Best MPH = 141.77