Weight isn't a big issue in terms of viewing - often heavier binoculars will allow a more steady view. Balance is the main issue when holding, and personal preferences as to grip etc. all play a part. The main issue with weight is whether you can comfortably carry them - there are various support options - wider straps, chest harness, shoulder holster etc. all of which have their fans and detractors. For me unless going on a very long hike weight isn't a big issue, but then I'm bull-necked and used to carrying camera gear...
I totally agree with Richard, balance is more important than weight, and ergonomics (like the focuser) can make a big difference.
I started with 10x50 Binos, to watch Nature and Stargazing, and I really had tough time to maintain them steady.
They were not well balanced, too "front heavy".
Later, I could afford a pair of SLC 15x56, Binos that are very well balanced, and were easier to hold steady (for me) than the 10x50 (I have quite large hands).
But while having these Binos in the Mountains is a pure joy (for Stargazing too), the focuser is very precise and too slow for Birdwatching, and they are big to carry around without a proper chest Harness.
Then I decided to buy a pair specific for Birdwatching. After trying 32mm and 42mm Alphas I couldn't keep steady (because too light), I ended up getting Meopta Meostar 12x50 HD.
And if I thought I was managing ok to keep the 15x56 steady long enough, boy the Meostar changed my "vision" of the world.
Nowadays, my SLC stay on my desk at home, and I mainly use the 12x50 now.
I brought the Meostar to Nepal when I helped monitoring the Steppe Eagle Migration in October-November, and have not regretted it a single minute. Spending so much time daily behind the Binos, the SLC would have been too heavy on that type of long use.
So in your position, I would choose the NL Pure. The SLC 56 are fantastic Binos, but heavy/Bulky to carry around, and you might find the focuser too slow for Birdwatching.