Small question as the new Cisco 5508 Wireless Controllers is out in the market which works on 802.11n technology, so how it is different from any 802.11g WLC in compare to speed,non overlapping channel and security point of view.
The 5508 has 8 gigabit port that can be put into a LAG bundle compared to the 2 or 4 that were available in the 4400's. The hardware architecture also has been changed to provide faster processing of packets through the controller.
Existing controllers (440x, 21xx, WiSM, etc) running v4.2 or greater already support 802.11n, as they support the 1252 access points. Also, non-overlapping channels does not change for 802.11n - it uses the same channels as 802.11a/b/g. Security options for wireless clients remain the same, from what I am seeing.
The big thing for speed, as was alluded to earlier, is that with 8 SFP ports, you can set up link aggregation to use up to 8Gbps.