I can suggest you to try out RadCompression for your minimizing the traffic. Check out this blog post
for example implementation.
You can enable output caching for WCF RESTful services. See here
for more details. Also .NET Framework 4 will came with a new assembly System.Caching (aka project Velocity) that can help here.
We are doing our best to have a preview of GridView's columns virtualization for our beta 2 release, targeted for the middle of October.
All the best,
the Telerik team