Pointy low rev misfiring when warm.

Hello all,

For a couple of weeks now I've noticed my SV runnning a little rough at low RPM. Similar to when I had a wet front plug and it was misfiring but nowhere to that extent. Like I say it felt a little rough.
Then on Friday on my way home the problem got worse to the extent that, regardless of speed and gear, when ever the bike was under 4500rpm it would struggle and misfire. This time feeling much more like when I had the wet plug problem.
On the weekend I changed the plugs, started it up connecting each plug in turn it check they both fired up and gave it a test ride up to the end of the road and back, everything seem hunky dory! (I know I've not exactly tested to the extreme here)
Today on my way to work, once the bike got warmed up the fault was back! and the same on the way home.

It seems the problem is only there once the bike is warmed up and only when revving at 4500rpm or below. If I'm below 4000rpm it almost feels like the bike wants to stall. I've not changed or done anything to the bike. Not washed it or used a different petrol station. In fact on my way on Friday I filled it up from a half full tank... yes the bike was misfiring before I put petrol in! The bike did seem to feel hotter than normal by the time I got to work today. I do ride in all (and I mean ALL) weather. The bike is an SV650 K3, stock apart from a Carbon Can Co. exhaust. I bought it about 9months ago with 10,000miles and I've done around another 3,500miles on it.

Has anyone got any advice on what it could be, what I should look out for or test?