I too am having the same slow issues when attempting to open files across my WAN. I've been using UltraEdit for years on my computer network LAN/WAN and I know precisely when this issue started. It started the day my computer was upgraded to Windows 7.
I also firmly believe this issue is directly related to the plethora of people complaining of very slow file access in Windows 7 via Windows Explorer when browser folders/files on other servers across a WAN. Example: Why is Windows 7 so slow in copying network files?
My own experience is the same; before when I had Windows XP my file browsing across the WAN was fast, and UltraEdit´s ability to open files was fast. We have a fast network. The once I got upgraded to Win7 my file browsing on servers across the WAN took a huge hit in performance and so did UltraEdit´s response in accessing WAN files.
Windows Notepad will open the files quickly.
I believe the issue can be alleviated by playing with the UltraEdit file settings, as mention previously above (turning off file detect is probably the biggest hit), but I edit files locally and WAN on regular basis and I do not want lose those features on local files.
IDM should add an UltraEdit ability to "play nice" and be less network-talkative when dealing with files on remote servers. If such abilities already exist then I would be happy to hear of them. The tricky part would be to identify LAN servers to WAN servers. I can access/edit LAN server files just fine; but when reaching to WAN servers (WAN servers on other side of the country as opposed to LAN servers in our own local building) that's when the hit happens.
As I've said, I've been working this scenarios for years and the WAN access took a huge hit when Windows 7 was installed on my computer, and UltraEdit was also adversely affected.