Agree with above^^^
How does the pack fit you and what are you going to be carrying in it.
If you can, bring all the stuff that you think you are going to carry, safety gear, first aid kit, snow shovel, extra goggles and gloves, extra clothing layers, emergency food etc... and what you will typically wear riding in some pretty foul weather, then go load that sucker up and throw it on your back (helmet too). If it seems to fit rite, go ahead and buy it. Will you ever carry a snowboard or ski's on you back? Will you ever need more space/carrying capacity or will this thing really carry all the stuff that you really should have on your back.
If this one "almost works" and there is another pack that maybe costs a bit more but really does what you want it to then buy the more expensive pack (or a cheaper one for that matter if it really works for you). Point is, I frequently fret over spending money on my "stuff" but once I have something that really works for me I have never looked back and regretted spending the money.
Oh ya, the hydration pack sip tubes pretty much all freeze eventually and then youre SOL and thirsty.
Oh ya, I have the smaller KLIM pack, bought it becuase it is well made and fits me fine, wish it was just a tad bigger and a few dollers cheaper, but all in all a well made pack.