Congrats on breaking the skunk streak, my longest was 27 boxes, 40 would put me close to asking that infamous question "is this worth it", haven't got there yet thank god. HH, Maverick.
Current skunk streak: 29 boxes
Number of 40% in last 75 boxes: 2
Number of boxes since last 90%: 112
I averaged a little bit over one silver coin per box in the first half of 2012, then it slowed, then it shut off like a faucet. I have gone from 6 boxes per week to 4 and I am considering dropping back to 2.
If dumping them is easy, and the pickups are painless, then I would trudge on. But any resistance on the dumping side, and I couldn't see how you go on like that!
Congrats penman - 13 keepers over 4 boxes is pretty decent (I'm ignoring the 29 boxes that came before it!). I agree with CoinFetcher - since you have an efficient system set up, no reason not to power through the skunk streaks.