Geoffster - Sorry to hear about your experience with the ZTechnik light guard! I ran an acrylic light guard on a KLR for a while and kept popping the bulb - air couldn't circulate behind it, too hot. Changed to a screen type and all was well. YMMV. Had a screen type on an R1200GS. No lens breaking but plenty of fine pitting.
I also downsized from an R1200GS to the F650GS twin and couldn't be happier. Lighter, great gas mileage, etc. While loaded for traveling I've ridden a few 500 mile days on fast roads and it was fine for me. Didn't seem that much different than same on the R1200GS. Being able to fuel on the side stand is a real plus on high mileage days with the bike fully loaded.
F650GS (Build Date 11/11)