Planning A few Big rides north of t' border in the next few months and a larger bag is required – what's the wisdom?

Large bag for what?

Do you mean for riding with?
If so havoc's are great 3L camelbak plus enough room for a full helmet pads, camera and lots more.

I'm not sure how it'd help your riding, but if you're keen then you can get weights and things to hang off it I expect. There's probably guides on the Internet.

Sellling this if you are interested 😉

http://www.singletrackworld.com/forum/topic/fs-camelbak-hoss-black

osprey talon.

I have the 22L and it is as big as like to ride with (can definitely overload it) although the 33L is also a popular choice.