It was mentioned in earlier postings that the new API is lightweight and passes the work all back to the server.  Based on that I had a thought that maybe this would make it sensitive to ping times and local clients would say performance is OK but WAN clients would report slow performance.  I did some testing of local vs wan and there is indeed a high dependency on ping time.  So using Firefox and issuing the new mail button on latest release the time from when the window appears to it can be utilized is as follows:

 

Local LAN - 6-7 seconds

WAN - 110 ms ping - 15 seconds

WAN - 160 ms ping - 23 seconds

 

Did Smarter Tools perform any performance testing on delayed networks representing the typical use case?