10,000 will not qualify as large. It is above 50,000 USD normally. For this and above you can ask for a rate and reference it in your money transfer. And your payment will be in the settlement instructions for an FX deal. FYI, I recently paid for my son's university which was a large amount but i used a credit card because it was just easier for me to do and the rate was good with the right card - in this case the BBL Infinite Visa. So it all depends.
No - we do not advertise because it depends on the deal and it depends on when. For 50 million it will be better than 50,000. If it is a future it will cost differently. It is complex. 10,000 GBP would not qualify as I said