Well, it's not the regulator but for the sake of £25 I'm glad I found that out.
Strange, the symptom you described was exactly the same as we had, if you hold it at 7000 for a short while and then gun it it died and then picked up. Fine if revved straight from off to the red line. It happened suddenly. My son had it out one day and all was fine, next day fault was there. We put in a new air K&N filter and oem fuel filter, but no change.
We swapped the following part from my 600 to my sons, coils, plug caps, carbs, ECU, fuel pump, and finally because it was the only thing left to change the rectifier/regulator. It was only when we changed the rectifier regulator did the problem go.
We put the original rectifier/regulator back, problem back.
The bike still has my bikes original carbs on it as it was to much hassle to change them back