It's my first post this site so I'm glad it's to help someone out.
I run a 3800 in our studio and have been using it for the past week as part of our Windows trial as quite a few of our friends and customers have been asking about similar issues. I'm currently running Windows 7 RC under VMWare Fusion on a MacPro and have installed Photoshop CS4, Lightroom 2.4, Nikon Capture NX2 and the Epson 3800 driver for 64-bit Vista as that's all I could find on Epson's UK site at the moment.
I'm glad to say that I can see know issues when printing to the 3800 from Windows 7, even when using custom profiles and colour managing the print via the applications so all looks good for anyone using Windows 7 until Epson get an updated driver out - presuming that they actually need to that is!
Hope this all helps, I hope to speak to you again in the future but if you've got any issues that you'd like to discuss feel free to ask or email me.
Replica Imaging Ltd