I rhavilan,
why you don't consider to install 3965 model instead 3865? the limit for de 3865 ap is not the throughput, is the use of the channel by the clients. With MU-MIMO in wave 2 you can work with more users, quickly and I think that in 3 or 4 years a lot of devices will works with ac .
I don't know the difference of money from 3865 to 3965.
Is a idea...