i've run my bullet on halfords classic 20/50 for the last two years. although it doesn't do all that many miles, it gets used a lot harder than most (and i do mean a lot!). it does thin out and start clattering when it gets overly hot, but i think any oil would do the same.
the oil is designed for cars, but being pre-unit (clutch has its own oil) and about as revvy as a canal boat there's no problems here.
absoultely no complaints with halfords classic, cheap and easily available.
BTW there's a bloke on ebay selling 6 oil filters for £14. that's cheap even by the standards of thumper club people!
350bullet