Personally I have stuck with the 13nm Astronomik since day 1. It has 97%+ transmission and thus long subs aren't as necessary, so 10min is sufficient on most sources with my red insensitive KAI11002 chip and 6" F7.5 apperture. It has been quite successfull at dodging moon light and light pollution (see examples below). I have found 10min sub exposures an excellent conmpromise to minimise the risk of issues during long exposures. I can't think of anything more frustrating than to take three 30min subs only to find the first had guide error, the second excellent tracking but a bright sattelite trail passed through the middle and the third a wind gust in 29th minute put a nipple on every bright star ...1.5hrs wasted
. If you are piggyback guiding, which is most likely with narrowband imaging anyway, long exposures can introduce differential flexure too so in a nut shell if you haven't got a great mount and tightly married guide scope I'd baulk at less than a 10nm Ha filter.
The other thing is Astronomik has just released their new filter design with lower reflection qualities to significantly reduce star halos in all Ha OIII SII Hbetta and LRGB filters.
Just some thoughts
Here are some example images done with the Astronomik 13nm filter and 6" APO. 13nm leaves some stars in too, tight and small though.
Eta Carina 3X10min FLI KAI11002:
http://www.pbase.com/strongmanmike20...66827/original
Lagoon 3 X 10min FLI KAI11002:
http://www.pbase.com/strongmanmike20...22109/original
Lambda Centauri 9X10min FLI KAI11002
http://www.pbase.com/strongmanmike20...22361/original
NGC 3576 24 X 5min SXV-H9 Sony chip (Gibbous moon)
http://www.pbase.com/strongmanmike20...66381/original
Mike