What will the traffic increase on our WAN be using GuiXT?

The WAN traffic for SAP screens is exactly the same, with or without GuiXT. For the scripts, it depends on how they are stored. For the following figures we assume that the user displays 100 screens in total, with 10 screens being different .
We assume a medium script length for the screens of 1K and a medium screen length of 8K. The percentage increase is based on the totally transported data on the WAN, not on the number of WAN requests.

Configuration A
Local scripts on each PC: No additional traffic.  
0% increase

Configuration B
Scripts in web repository or ftp/http server, + using VersionNumber: Almost no increase if no script changes (only 1 script loaded for logon screen).
<  0.01% increase

Configuration C
Centralized scripts in web repository or ftp/http server, no VersionNumber, but local cache active: 1 script access for the first time a screen is displayed. Increase of 10*1K = 10K of totally 800K.
< 1.5% increase

Configuration D
Finally, worst case: Centralized scripts, local cache deactivated in profile. 1 script request for each screen. Increase of 100*1K = 100K of totally 800K.
<15% increase