Did the FS combo last May for 5 nights and it was perfect! Would highly recommend 2 nights Sultanahmet and 3 at Bosphorous for all the reasons already given. As an aside, we had some of the best service ever at Sultanahmet. They greeted us like we were members of their long-lost family (I still wonder whether they confused us with some VIPs, but the service carried on in this fashion throughout our stay). The Sultanahmet courtyard restaurant is delightful for breakfast and the Bosphorous terrace is very glamorous and gorgeous (I still think of my breakfasts there, sitting under a shady canopy, the white marble, sparkling Bosphorous and the thousands of red geraniums). Concierge service at FS Bosphoros was also very good. We all loved both of these hotels.