no one has your particular iPads and these could be characteristics of the devices you have in front of you. Do you have a meter for measuring sound pressure levels? 5-10dB is a lot.
Well I have the eldest son here at the moment with his iPad2, and can confirm the volume from both his iPad2 and my iPad3 are the same, the comparison test was after installing the same ripped film onto both of them, which was pretty much the result I expected, my iPad3 is definately as loud, infact I thought it was a fraction louder, but my son reckons they sound the same so they probably are. It was the 1st time he had seen a iPad3 in the flesh so to speak, he acknowledge the screen did look much sharper, but he say's he's hanging onto his iPad2 a little longer before upgrading.
I also took a look at the white balance on both versions, and TBH the white balance was not far off on either of them, with both showing decent pure white screen without any noticable colour hue. (both set to 50% brightness) I would say when watching a film the colour may just be a touch warmer on the iPad3 but you really had to look close to tell the difference, though it did look slightly better of the 2 ipads, just a fraction sharper. I showed him a blu-ray rip I did a couple days ago, and of course the difference was very evident, but I doubt I shall be doing many more due to the increased file size. (Jumped from 1gb to almost 3.5gb)
My previous iPad 1 which my wife uses, may just have a fraction of green hue, but it's barely detectable and in any case may just be my imagination, as it too looks pretty good to me. However one thing is certain, the sound on both the ipad2 & 3 are definately better than the first gen ipad, I suspect probably because the sound comes out of a small slot actually on the edge of the ipad 1, sound quality.. tone wise is better on the later 2 iPads too.
When I got my iPad3 last Friday (16th) I noticed quite quickly that my iPad 3 was noticably faster at loading web pages, when compared to my iPad1, so we did a quick test with that too, just to see how the 2 & 3 compared, both were much faster than the iPad1, but less difference between the ipad 2 & the 3, with the newer model however still loading the pages a little faster, but not such a noticable difference when compared with the original gen 1 iPad.
I've certainly not noticed any issues regarding uniformity of colour across the screen, difficult to imagine how that could happen on LCD panels, other than uneven backlighting... though background room colours/reflections can create some funny tricks sometimes, very strange one though... but certainly pointing to an imbalance in the lumination of the backlighting.
Ultimately, if your concerned about the issues you mention, then I can only suggest you take advantage of Apples no quibble 14day refund or replacement policy, something like a tiny bit of backlight bleed at high brightness can be tolerated as under normal use it won't be visible, but bad pixels or dust under the screen, or visible uneven screen lighting, then I would certainly say it warrants being replaced.
IMO, screen brightness/colour uniformity issues would suggest the backlight being brighter one side than the other.