You have it setup wrong. Whats going on is you are setting up the RAID0 pre Windows install so its making a 64GB RAID0. In order to use part of the SSD for SSD Caching, you need to install Windows on the SSD then install IRST and setup the SSD caching there, not before Windows is installed.http://download.intel.com/support/chipsets/sb/intel_smart_response_technology_user_guide.pdf
I at least assume thats what you are attempting to do.
I have Windows on a 80GB Intel X25-M and my games and data are on 2 500GB in a RAID0 and have no issues like you are having.