I worked an entire summer surveying bighorn sheep (glassing all day long) with my 10x42 non-hd vipers and have used them for western hunts the last 6 years. They work well for me. I'm sure the new HD glass is even better. I did get headaches, but not from my binos, but from the cheapo bushnell spotting scope I was using. Vipers are good glass...not swarovski good, but for the price they are excellent. I always advocate buying the best glass you can afford. For the price it'd be hard to beat the vortex in performance and warranty.
I would recommend going to the store at twilight and looking through each you are considering, comparing them side by side. This will give you a better idea what you've really got.
Cheers,
Matt
ps- On headaches- It is important to get the focus properly adjusted to each eye independently. If not you will get headaches no matter what the glass. Also, for long glassing sessions it helps tremendously to mount your binos on a tripod to keep them stable. It also allows more efficient spotting of movement as well as being easier on your eyes.