So, I have done my research on the 511 and 512 and it really comes down to the difference in cost, length, weight and battery life. I just cannot decide and need a push in the right direction,

I like the 'idea' of the 512 using AA batteries for longer life, but it comes at the cost of 3.5 or so ounces and a 1" longer sight taking up room. AND, wil it really matter that I get much longer battery life than the 511 for the everyday casual user? if not, seems like the lighter, cheaper, shorter 511 is the way to go.

which way do I go, which way do i go...

AA

Get the 512.  The 1/3 N batteries are way more expensive, much more difficult to find, and have a shorter battery life in this sight.  You have plenty of room for a BUIS with the 512, which is about the same length as an Aimpoint anyway.  The 512 is the only way to go with the EOTech (non-NV).

On the 552 the optics electronic check that takes place with each startup is predicated on AA batteries. Doesn't give good poop otherwise. If this is important to you and if the 511/512 setup is the same you might want to go 512.