Just completed a 5-night stay on points and used a SNA for the full stay. I had booked the standard atrium view with King and was upgraded with the SNA to the Premier, Guest room, 1 Queen(s), Galata Tower view, Terrace. I was happy to have the upgrade but not happy on the bed size downgrade, so I sent an email to the property asking if they had the same room category with King bed, of which they did have 1. I was given room 710, which I think is one of 4 rooms along the back of the hotel, with 710 being on the corner. The room is perfectly adequate in size but it's not big. It's nice to have the terrace which has a functioning whirlpool tub, and overlooks the busy (in a good way) Mumhane Street below.
The hotel staff were all very pleasant and kind, always name checked and asked how my day was going. Room cleaning was good. I was visiting with my wife for her birthday and they sent a pre-arrival questionnaire so they had put a cake and balloons in the room upon arrival. There was also a Bonvoy Member recognition event in the cocktail bar downstairs where you could make your own drink with the bartender as tutor.
The only things that I'll criticise was (i) the price of champagne, of which I would have like to have had in the whirlpool but it was not to be - €350 for a bottle of Moet Chandon! I think it was less at the St Regis Maldives (ii) turndown service didn't refresh things like drinking glasses etc, and (iii) slight smell to the room that I think is the drains(?) but quickly dissipated with opening the window. That's often the way in big cities though.
Construction at the Peninsula is done but there is a building directly next to the hotel that remain under construction. I only heard a bit of noise during breakfast one day as I was out exploring most of the time.
All in all, easy to recommend as a base to explore Istanbul. I went back and forth about staying in Sultanahmet or not, and I was really pleased tin retrospect o be staying across the bridge in Karaoy. It's quite a hip neighbourhood with lots of coffee bars, kabab shops, bars, restaurants etc. It's a 15-minute walk from the hotel to the other side of the bridge, or you can buy a travel card and the fare is I think 15Tl.