My math was a bit off. I redid it with the platinum bonus and arrived at ((275*10)*1.5) = 4125 IHG points if booked with the CSR, or an additional (275*5)=1375 extra if booked with the IHG card. This calculator agrees with my math as well. I'll go with CSR as I had completely forgotten to add the platinum bonus - I see now that it's still a decent amount of IHG earnings, and missing out on the card bonus won't affect me much. Thanks!