D-Link DIR-825 :: Performance Better Than 655 In 2.5ghz Only Mode

We've been using an 655 in an NGO office that has grown to 20+ computers in two buildings (next to each other). The 655 doesn't seem to be handling that many clients very well so I want to get another one (perhaps a more powerful unit). We will stay operating on 2.5Ghz, have one of the units act as an AP in the other building (too bad we can't bridge with these). Most of the router activity is LAN based (server, etc). Our Internet connection is only 256kbps satellite (and is proxied first through the server). But the LAN performance is not good when many clients are active and some services on the router will freeze and require reboot several times a week, assuming b/c it's overtaxed.

1. know if the 825 will perform better in in 2.5ghz only mode than the 655? Seems that it has more RAM. Newer processor too? The tests I saw online showed that the 655 outperformed the 825 in simultaneously connections, but I assume that was probably in dual mode. I want to know if the 825 will be better in 2.5ghz only mode. We won't need 5ghz mode.

2. Is there another newer DLink I should consider that would provide better capacity and throughput on 2.5ghz only? However, it is ciritical that we keep the same feature set for security (IP based access control rules to various IP ranges on the Internet).

3. It would be awesome if some DLink supported even more sources and/or destinations per access control rule. We use these extensively and the 655 B1 2.01 build has several bugs for access control rules. Is there any DLink that has more robust access control or is it about the same for all?