I'd look for faired bikes myself. The GSX650F can be had for quite a bit under your budget and you can spend some money on upgrading the horn, headlights and adding in things like heated grips and other decadent luxuries. Top box is a good one as is a TUTORO / Scottoiler. The tank range of that bike is also very good but the MPG is (good, about 50-60mpg apparently) not up to the indecent figures from the Duke.
I'd avoid KTMs - a breakdown guy told me recently they're hideously bad for breaking down.
For christ's sake, I've just got off the bog and I need another shit. Hang on.
I think KTMs are just high maintenance rather than intrinsically unreliable. The 690 Duke would be amazing fun on the B roads though but a naked bike becomes less fun during winter and more of a pain. Faired bikes make it more tolerable. I'd also suggest Suzuki parts and servicing should be cheaper.
The CBR600F comes in a sportier version as well which may be a bit uncomfortable depending on your physical fitness and so on. Make sure you're aware of the differences in models and try sitting on them.
You'll have to keep the Suzuki cleanish during winter and ACF50 would be a big bonus during winter. It's not just about finish, it's about avoiding fasteners having to be drilled out during services and costing more money and so on.
The Street Triple is a good bike and a lot of fun but again it's naked and that can end up just getting annoying during a commute.
As your budget is quite decent, you might consider a BMW F800ST. My BMW has barely any rust (couple of nuts and a fastener or two) through winters where it hasn't been washed and the exhaust is completely clean (usual weak spot in winter). The F800ST has a belt drive which will relieve you of chain maintenance and possibly save you money (a new belt is very expensive but it needs to be changed at very high milage, so it sort of evens out). BMW servicing is very expensive usually but these bikes have a reputation for being cheaper to run than most. I think that's partially because they can get almost all information from plugging it into a computer (even if the valves are within tolerance) but that level of complexity leads to expensive costs if a sensor fails, etc. They're known for good handling and decent fuel economy. I'm strongly considering one myself, especially as insurance is so cheap on them.