I have some prices to report
1) Approx 5% on top of a BA sale. SEA-CDG was $2724, offered to me over the phone at $2593
2) Approx 11% off of KLM-marketed, DL/AF operated flights (also SEA-CDG). Retail was $3077, and was offered $2717.
Also, I am happy to report that booking online at Amextravel.com now shows IAP results when you log in! However, not all airlines are participating. The Skyteam ones all showed up (#2 above) but nothing from BA, I had to call for their price.
Final news is that the $39 booking fee was not assessed on my invoice, perhaps it's because Amextravel.com isn't the same as Platinum Travel Services? I mostly booked online because it is easier.