Re-posting in this thread - My exchange rate at point of sale on AMEX was EUR1.3966 per £ - could there be a benefit when it is refunded?! I think it has dropped about EUR0.04 since then - which isn't a bad amount over a £4,500 spend...
** update - two of my £827.35 bookings have been refunded - £835.20 showing cleared on statement.