Since you're not using the bin for hunting, a non-WP or WP but not submersible porro will work.
For dawn and dusk, twilight factor kicks in, so a 10x will show you more detail, provided you can hold it steady. For many people, 8.5x is the best compromise possible and so is 44, which gives you a bit more light while not adding a lot more weight.
And as eluded to above, if you can use a 6mm or 7mm exit pupil, there's little point in carrying the extra weight although the longer FL will reduce some aberrations, but for your purposes, that seems less important than light grasp (that you can actually use) and high light transmission.
Light transmission numbers are hard to come by. The best porros beat the best roofs in that regard, but the gap is narrowing with dielectric prism coatings and the latest and greatest gazillion layer AR coatings on roofs.
If you are "under 40," a Docter 8x56 will soak up photons like a Bounty paper towel sucks up water. I had a "aus Jena" (Zeiss East) 8x50 Octarem, and even though it only had MC not fully multicoatings, I swear there was a tiny gremlin inside the bin shining a flashlight on whatever I looked at. Doctor bought Jena and their porro designs are very similar, but with FMCs. Unfortunately, they no longer make the 8x50 model, which had a 7.4* FOV. The 8x56 model has a 6.3* FOV, which is a bit restrictive, IMO.
I used the 8x50s to look at nocturnal flying squirrels, owls, possum, and other night critters and they worked very well for that purpose.
The Doctor 8x56 has large objectives and high light transmission (the numbers on allbinos might be a bit exaggerated, but they are still up there). Not sure what they cost on your side of the pond, here they are within your price range ($900).
Here's a review:
http://www.allbinos.com/81-binoculars_review-Docter_Nobilem_8x56_B_GA.html
If you like the Minox brand, you might be able to find a pair of their 8x44 porros. Lighter weight than the Doctors, and half the price or less. Still high light transmission.
The 8x44's FOV is also a bit restricted (6.3*) but so are the much more expensive Japanese made Minox HGs, particularly as you go up in aperture.
I haven't tried this model, but I did try a Leupold 8x42 Cascade porro, which is similar in design (internal focus like roofs). No sucking in dust, pollen, and cat hairs.
On the roof side, the 8.5x44 Kowa Genesis is ranked #1 by allbinos in the 8.5x44-45 category. It has ED glass for extra contrast, which is something you want in low light conditions. A wider FOV at 7*. But Beware of the Rolling Ball. These binoculars have low pincushion distortion, so for some people, they will produce a curvature in the image that will result in a strange perception while panning with the bin.
IOW, these you'd want to try out before buying or buy from a store with a generous return period since it might take a few days to adapt to the "rolling ball effect". I haven't tried these bins, but I am very familiar with "rolling ball" but also with the boost in contrast and color saturation that ED glass provides. If you go for the Minox, choose the "APO" version for this reason.
These are a bit over your budget, $1,200-$1,300 in the US.
Here's allbinos review of the Genesis:
http://www.allbinos.com/156-binoculars_review-Kowa_Genesis_8.5x44.html
Here's Holger's review of the same bin (Prominar XD and "Genesis" are the same bins):
http://www.holgermerlitz.de/kowa85x44.html
Here's Renze's product review on BF:
http://www.birdforum.net/reviews/showproduct.php/product/240
Another user review:
http://www.cloudynights.com/item.php?item_id=1754
Not trying to push the Genesis, but there are more reviews of them. Try to read more than one review of the bin you're interested in since no matter what the numbers say, people see things differently and some reviews can reveal aspects of the bins that another review might ignore.
For example, no mention of "rolling ball" in the Genesis on allbinos, only praise for its low distortion whereas Holger's review mentions it.
Some bins you can put up to your eyes and know right then and there they aren't for you. Too heavy, don't feel right in your hands, uncomfortable eyecups, too much "distortion" at the edges (pincushion or field curvature or astigmatism), not enough pincushion, they smell funny!
Other times, you have to live with the bins for a few days or weeks before knowing if they are keepers. In your particular case, you need to use them at dawn and dusk to find out what's what.
Also check out Meopta Meostars in the 8x56 model ~ £800.
Brock
