Straight water is best for the trackie mate - in most situations. If you are racing the bike, then you can't use glycol-based coolants *at all* anyway. There are some additives (expensive) to raise the boiling point of normal water, but its a woftam I reckon. If you only do ride days though, normal coolant is not a problem.
Rob's advice is spot-on for your problem Bushy - try that first before you spend hundreds at the workshop.....and if you do need a *new* radiator - try and get the old one repaired first if at all possible. This is a way cheaper option, all it may need is a spot weld here or there in the core to plug some holes.....
Have you pulled the oil-filler cap off yet ?? Or drained the engine oil ? It may be worth doing this, just to see if the oil is milky....

- if it is, then you have blown a head gasket...
