Here's my question: should I rent the Souris River Q17 or the Souris River Q18.5 for my upcoming Quetico trip?

The group will be me and a friend (both <190#), and my hound (<40#). I do know that everything will fit in the Q17 - I've done it a few times before. We're not doing any really aggressive portaging, so the extra few pounds doesn't matter. What I want to know is which is the better option for paddling big water, and which is the better option for fishing out of while unloaded?

We'll be spending time on Pickerel, Batch', Nym, et al. And we're not moving camp every day, so we'll be fishing out of the boat a lot with no load.

My outfitter has always recommended the 17 in the past, but I recently had a trusted veteran advise me to take an 18.5. I thought I'd get opinions here for a tie breaker.