Andy,
Seems you're spoilt for choice. Lots of great bikes would do the job. The Two Up aspect does narrow things a bit, but still plenty of good bikes could make you happy ... and even offer performance close to your FZ-1.
BTW, a Brit friend of mine (lives in USA) did a Full Euro trip on his FZ-1. Shipped the bike over, rode about 25K miles, shipped it home. All of UK, Europe, Eastern Europe and more. That FZ-1 has been around. He's even ridden on dirt roads on some of our local club rides here, near San Francisco Bay area. A great bike!
Tony on his FZ-1 in Death Valley area. (this ride was 85% tarmac) Tony can ride it ANYWHERE! ... and keep up with
our Dual Sport bikes.
But for two up, I'm not sure the FZ-1 is ideal. Bit more room might be nice?
Perhaps try out a few bikes? The Super Tenere' is not a bad choice, but I'd bet a BMW R1200GS is more comfortable two up, maybe better "all round" bike? ... if you can handle the "service issues". Both GS and Ten are pricey machines.
A lower budget (and very good) option would be the new 2014 Suzuki V-Strom DL1000. Does it ALL well at a lower price than BMW, KTM or Yamaha Tenere'. I owned original V-Strom, stellar reliability and performance. 90K miles.
Inexpensive to run and keep on the road compared to BMW, KTM, Aprilia, Guzzi.
If you've got the budget you must try out new KTM's. Stunning performance but WEAK in comfort and service areas.
Other bikes to consider:
Triumph Explorer 1200
Yamaha FJR1300 (latest updated version)
Moto Guzzi Stelvio
Aprilia Capo Nord
Ducati Mulitstrada 1200
Honda 1200 Crosstour
2nd hand bike would be much less, so consider that too.