Grade Pay for 8 years CAS benefit?

I am an officer of a Corporation in West Bengal under pay scale Rs. 9000 – 40500 (Grade Pay: Rs. 4700). In our Corporation, there is neither any promotional avenue for our post nor any sanctioned post corresponding to Grade pay of Rs. 4800. As such, please let me know that with the CAS benefit of 8 years whether my grade pay will be Rs. 4800 (i.e., the next higher one) or Rs. 5400 (i.e., an attainment of an additional increment due to non-functional promotion). Regards.