The design you have suggested is similar to the APEX jQuery Mobile implmentation, however this is not currently available in FOEX. We are looking at different dynamic loading techniques for future versions of FOEX but there is no immediate workaround.
You may be interested to know that the FOEX demo environment is Oracle XE running on a small amazon instance (1 CPU core) in ireland.
However there are many factors that affect performance. Could you please do the following:
1) Please put the page in debug mode and send us the debug output for the page load and also the grid data AJAX load.
2) There is a caching option within the FOEX Settings plugin and within region plugins like the grid which should be enabled whereever possible in production. This caches the meta data for the grid so that it does not need to be read every time. Please test this feature and benchmark the load times before and after. Also understand that you do not want to cache mete data during development since you are making changes all the time.
Once the page is fetched there is also the HTML rendering time. We are upgrading to Ext JS 4.2.2 in the next major release of FOEX which has a significant reduction in HTML rendering time compared to the current 4.0.7 version which we are using.