It would be considered a downgrade. The ASUS X200CA has the Intel Celeron 1007U CPU which is based on the Ivy Bridge generation CPU. They Asus Transformer has the Intel "Bay Trail" generation Atom Processor Z3740.
Despite the fact that the Z3740 is a quad core CPU, there is a decent amount of performance difference between the Celeron and the Atom CPUs. The Celeron would be considered a powerful dual core CPU. I would guess-itmate that each Ivy Bridge core is over than 2x as powerful as a Bay Trail core.
Additionally, you would be limited to 2GB of RAM which is rather lacking in my opinion. Windows 8.1 can run with only 2GB of RAM, but if you are the type who likes having a lot of programs open, or many tabs open to browse the...