It's always going to be a minimum of 2 trips otherwise you'd forget your guitar. My routine on arriving at venue is, trip 1 with cab of choice or both (15" and/or 410), trip 2 for my guitar with the Orange head over my shoulder in the man/handbag.
As for volume, I have ashdown cabs and with either it is amazing ( trouser shaking, chest thumping), very deep and rich but plenty of high if that's your thing on the eq; with both cabs it would cope with a stadium.
Top gigging tip: when packing up always leave the big cab unsupervised and lock the guitar and head up in car first, unless of course you are hanging around post gig, in which case keep them with you as they are very "walk off-able"