Hi Richard!
Welcome aboard; I think you'll like it here! What an entry...a brand-new, lovely Sherpa! Wow.
I would suggest using the bike as much as possible during the trial period so you can see if it is truly right for you in practice. Thorn do a terrific job sizing bicycles to riders, but there's always personal preference to consider as well. My Sherpa was spot-on, but I was in a similar dilemma of "qualifying" for two frames I could ride for my Nomad, and after talking with Andy Blance decided to go with the larger of the two at the expense of a wee bit of cargo capacity. I'm really pleased with the decision and the fit.
Still, I figured on some time and small adjustments to get things where I needed them to be perfect, and this proved to be the case. I budget for this on every bike I've bought. While the bike fit as-delivered with a longer stem and deep-drop anatomic 'bars and the brake levers positioned high, I found myself happier with compact drops, a shorter stem, and more conventional lever placement. I knew the fit would be a bit more challenging using drops on a "Medium" top-tube frame, but it all worked out and I could not be happier. One delightful side benefit is I now find myself positioned well within the bicycle's wheelbase, so I feel like I'm riding *in* the bike than *on* it and all works wonderfully.
I hope things will settle in to a *perfect* relationship for you and the bike. If you have any quibbles or niggles, I feel confident suggesting you contact Thorn, as they really do want you to have a happy experience. Of course, if there's anything the Forum membership can suggest from personal experience, please feel free to ask. Your bike looks terrific!
All the best,
Dan.