Rapha, nice but a bit pricey?

Most retailers (online or not) will only check rates daily or weekly depending on their payments provider.

Bear in mind that regardless of the advertised rate, the rate that is applied is the one that is billed... usually in the currency that is local to the billing system in use.

I'd go out on a whim and guess that if you set the currency to GBP and paid in that, it would be billed in that, and your local bank would apply the most recent rate and you'd get your discount.