Are you only using a single windows machine to test, or are you testing with another windows machine as well?
Chrome has a developers tool called "timeline" that will show you a breakdown of what is causing the page to load slowly. I'd imagine it has something to do with the way your windows machine is configured, such as antivirus or browser security plugins. I would record the actions of connecting and see what takes the longest time.
WebDirect responds pretty much the same to all browser requests, any incompatibilities are usually a result of the browser not being able to parse the code correctly (EG IE6 doesn't support HTML5). So identifying what's different about the browser is the key.
Another thought is that possible the DNS server your windows machine is using is slow. Are you connecting via the IP address?
Thanks Mike I've found the culprit. Sophos Anti Virus!
Disabled on access scanning on my machine and some other windows machines and the page loads fine. Wonder if there are other anti virus that affect it in this way.
Can't believe I didn't try that earlier. I'd done the usual disabling Windows Firewall.
Sure, it's a good reminder at least to check things out on the system.
Not familiar with sophos, but most AV programs have a whitelist that you can add to bypass filtering.