Don't obsess over ethanol, Mark. While it remains in suspension within the fuel it will be harmless. It is only when the fuel absorbs water that the ethanol separates out and starts to cause problems.
If you are going through a tankful at least every four to six weeks, then you should be okay. It's difficult to say exactly how long the fuel will last because so much depends on the ambient temperature and relative humidity. Safe to say, though, that, if you're laying up the bike over winter, you should either completely drain the fuel system or add a fuel stabiliser specifically formulated for ethanol fuel.
Alternatively, just use Esso premium, which, in most of the UK, is ethanol-free.
Have a look here for more information on ethanol
http://www.ukmonster.co.uk/monster/s...ad.php?t=54542