8X40 are a great choice for a general all round binocular. I've a pair of 8X45s that have been with me for 15 years and always rendered good service. They will be fairly light, compact, easier to hold steady and have a field thats wide enough to follow flighty birds.
I think $400 is also a reasonable amount to spend to get a pair of binoculars that will be of lifetime service. This price is in the middle grade of binoculars, much better than the cheaper stuff that costs one third as much but not quite as good as the fine stuff that cost 3 times as much. A nice place to be.
As far as brand goes, I'm partial to two brands: Nikon and Vortex.
Nikons are an old school company. I own a pair of 12X50 AEs that I use for astronomy and birds at long distance. Nikon offers a good warranty.
Vortex are a newer company but are known for producing great glass. Their warranty is lifetime and they will replace them for any reason - a great warranty from a company that has full confidence in their product. I just looked on the net and a pair of Vortex Viper8x40 roofs, argon purged (waterproof with no internal fogging), rugged (built with hunting in mind), ED low dispersion glass runs $439.
I have a 6X32 Vortex Viper binoculars that I love. I didn't mean to buy them until I looked thru them then bought them on the spot. They are great glasses and a wonderful window on the world.
I think you are on the right path- tho if possible I would urge you to go to a Cabbalas / Bass Pro / some other hunting/ fishing / outdoor chain and spend an hour or so looking thru binoculars (they have lots of models)