I just got this router and it is indeed very slow to bring up its pages on the 2.02 FW. I have the DIR-655 and it's super fast. After upgrading the FW to 2.03->2.05->2.06, it did improve just so you know. However, you may want to get prepared for the possibility of NOT being able to even access the UI at some point after you upgrade the firmware. I'm in the process of trying to resolve that issue, but if you upgrade, the UI response will definitely improve.
Note that the 825 does have a very annoying "waiting" pages after many if not all commits that force you to sit for x number of seconds until you can continue on that the 655 did not. Not sure why the 825 software can't just commit immediately like the 655, but I don't know the internal workings...