I recently passed my DAS and have been knocking about on a Yamaha WR125X which is a nice little bike (and it don’t really look like a 125 tbh), I use it to commute into central London everyday and it is absolutely fine for that. I kind of ride it like I stole it I suppose, I always keep up with all the other more powerful bikes between all the traffic light, so for my commute this bike is fine. It costs £16 a year to tax it and I get about 130 miles out of a full tank of petrol (£8). However, dual carriage ways and motorways is a different story, I don’t get much over 60mph lol, and I can feel myself yearning for more power.
I have been looking at the Suzuki DR-Z 400cc SM mainly because it is pretty cheap and has loads of after market support, but I wonder if it is worth going for even more power - like a 600cc? I think I’m pretty much sold on supermoto cos I am very tall and I like the high ride height and upright riding position, plus they look the nuts 
Just wondered what others can recommend, KTM, Husky, whatever? I’m not too bothered about the make, just want a good SM that will also have a bit of oomph on the motorway. Cheers 