New backpack strap placement on Synapse 19?
Eh! Upon further reflection, I would highly recommend getting both, maybe in different colours, and seeing which works best for you. It's a pain in the @$$, I know, but it's the surest way of making sure you're getting what you want.
Firstly, it's hard to predict whether the current strap will fit your build, based on what I've read on the forums so far. Secondly, as you might have gathered from my long-winded posts above, there are lots of factors to consider when deciding which size to get. I feel these issues can be discussed endlessly in the abstract! The best way to find out what's perfect is to load up a bag and carry it around the house. Run, walk, squat, bend down, cook dinner, bike, etc. with it on, while carrying different loadouts. Or something.
The only real downsides to getting both are 1) a real risk of keeping both; 2) paying for return shipping (but I hear it isn't too much). :)