Fletch,
Not sure if this is coming in to late and you have already bought a bike, but thought I would chime in.
I own a V-Strom 650 and love it. Being a big guy just like you, I have had no problems with its power. I live in the Colorado Rockies at 9,400 feet. 7 miles east is Loveland pass that tops out at 11,990 feet. I did an experiment one day to test the power of my Wee-Strom. I loaded up 200 lbs in my panniers and top box and took a ride to the top of the pass. Keep in mind, my big arse weighs in at 290 lbs and I had no pile-on. The Strom rode very well up the "hill" at 65 mph and that was in 6th gear, churning 5,000 rpm's and the throttle nearly maxed. I never bothered to kicked down into 5th gear and twist the throttle harder. I have no desire for speed, but it's nice to know theres a little more umph (an additional 5,500 rpms) in her to be able to pass someone when needed. This leads me to conclude that a V-Strom 650 will be adequate for you, your S.O. and gear. Not sure about in the UK but here in the U.S., the 2007 V-Strom 650 will have an ABS brake option for only $500 more. What a deal!
The best mods I ever did to the bike was exchanging the front and rear OEM springs with much stiffer Wilbers springs. My pre-loads are set "soft" when its just me and I am left with the full adjustment to work with when I load her up. These bikes right off the showroom floor are set up for a single rider that weighs a mere 180 lbs. and no luggage. Before my spring swap, my preload was maxed and it was still to soft. Big guys like us are just not in the scopes of motorcycle engineers.
Other mods and additions I made:
--Wolfman Explorer Tankbag - Excellent! Looks like it was made just for the strom's tank!
--Happy Trails Panniers and top box
--Motech Skid plate (piece of sh*t) - get an Adventure MotoStuff plate or a Pat Walsh
--Motech crash bars - I like the looks of these, but have not "tested" them yet and hope not to anytime soon!
--Scott re-useable oil filter - none better!
The Wee-Strom is not an Interstate bike and its not an offroad bike either. Its best suited for the speed of paved 2 lane highways, the back roads and mountain passes. More the speeds that you are likely to encounter on a long trip that is not in the USA or Western Europe. Gravel is fine, but I would consider better tires than the trail wings. If you are going for long stretchs of the loose stuff, maybe TKC's?
You received great advice from everyone above! Good work guys! I second the notion of avoiding Touratech, to pricey!
If you go for the Strom, good sources for info. and outfitting her are -
www.twistedthrottle.com
www.amotostuff.com
www.stromtrooper.com
http://11109.rapidforum.com/
http://motorcycleinfo.calsci.com/VStrom.html