I have 6 - S7's and have won 2 blocks with some pool mining in between.

"height":410375,"hash":"000000000000000006180b6ce488ca2a779ed6ee460363489a04716f5f371c23"
"height":383960,"hash":"000000000000000001f1506aa837ff75b70536209787600028eda329f80d16d0"

Whenever you solo mine the risk goes way up. You could go months with mining a single block, all the while the difficultly continues to go up. At this point I would stick with pool mining with the halving coming up. Over the long run it will always even out.
The first block I won only took 4 days of solo mining, but the second took over 3 months.