Duck, thanks for the info on the Odyssey PC680, which is available in SA, about the same price as the BMW battery. It has an impressive spec and I may well go for that. However, for around half the price, the Yuasa YC20-12 is available, also a sealed, maintenance-free unit. I attach the spec sheet for it and I'd be interested to hear if anyone has one and what they think of it.
As mentioned, my bike is stock, non-ABS and I don't intend to ride at night so a 20 AH battery should exceed minimum requirements I think.