Boltaz, those settings look decent and are probably not the root cause preventing you from achieving the desired throughput. What are the receive signal and SNR for that particular SM? Is the RF performance conducive for modulation modes that will allow the 25/5 speeds? Are there other users that are also sharing the capacity of the AP at that time? I would recommend investigating the RF performance first and also running a link capacity test from the SM. Note that doing so will consume all of the AP's resources at that time.
Also, you may want to adjust your burst size accordingly based on how long you want the burst duration to last. There is a post on the forum that explains it along with a link to a burst bucket white paper that will help you calculate the burst size here:
http://community.cambiumnetworks.com/t5/PMP-450/burst-bucket-and-sustained-datarate/td-p/48424