I posted this exact message a little over a year ago when someone asked about the OV cabins on deck 3.
"We've stayed in the OV cabins on deck 3 on three separate cruises. We loved it every single time! It was awesome being so close to so many places we wanted to hang out at... Martini Bar, Cafe al Bacio, World Class Bar, Passport Bar, MDR, etc. And we never heard noise from outside our cabin at all. The first time we were in an OV we were further down the hall from the public areas but after seeing how quiet it was we moved to the first couple of cabins down the hall from guest services. It was incredible... we were less than 100 steps from our table in the MDR! I would never hesitate to get an OV on deck 3."
As far as the closing time for the casino... I don't have much experience in the casino but from what I've read recently I've seen it closing as early as 11pm and as late as "late". Not sure how to define late.
Have fun on Silhouette in April. My wife and I will be there in April too for a B2B.