I have Docter Nobilem 8x56 for low light observation,
and it is performing very well. Important for low light observation
is maximal dilatation of eye pupil, which is in relation with age, and mst
match with exit pupil of binocular.
Older hunters buying 10x50 format because of 5mm eye pupil at the age of 50.
Maybe you know this sites with reviews:
http://www.binomania.it/wordpress/?p=3117
http://www.allbinos.com/allbinos_ranking-binoculars_ranking-8x56.html
Light transmission is important for low light observation,
and I think that 90%+ is required for good vision.
It can be achieved by porros at better price than roofs,
but there should be some exceptions on the market.
Roofs are better with Abbe-Koenig prism like Zeiss dialyt, victory 8x56
but top Schmidt-Perchan roof prism with dielectric mirror should be also good
(Swarovski SLC 8x56).
In Slovakia hunters buying mainly Steiner Ranger Pro 8x56, because of price lower than 500€ and good design and mechanical durability.
Maybe Fujinon FMT 7x50 should be very good, but with lower magnification.
Magnification is important on longer distance ~500m.
I have friends which buyed Nikon Action EX 7x50 at good price, but they are not so critical low light observers.
Best regards Kestrel