I've done 3000 miles on a 2003 F650GS since I bought it in mid-May; this is commuting, visiting clients (I am a social worker), and weekend ride outs.
I absolutely reccomend it; 46ftlb of torque is punchy enough for the twists and turns of urban riding in the UK, and the suspension makes light work of potholes. The bike is *very* stable through corners, indeed I scraped the pegs on both sides within 600 miles of ownership. Build quality will stand up to our weather as well.
I've also ridden quite a lot two-up. I am 16st (102kg?) and my g/f is 11st (75kg?) and the GS will still do 95mph with us and a top-box. OK, so that's revving the nuts off it, but the point stands.
Buy the GS. The UK KLE is acknowleged is just about every UK road test as an absolute dog, and seems to have been (re)introduced by Kawasaki as a mere stop-gap until the launch of the Versys (an altogether different proposition).
I like the 650GS so much I'm possibly shelving my plans to upgrade to the F800 series (though I may add a Blackbird as a touring bike instead).