I think i got the answer. In an OFDM system bandwidth is calculated is no.of occupied tones x (sampling rate/total tones)... so for the system employed at texas university the bandwidth was 64 x (100x10^6/400) which comes out to be 16 MHz.
So I guess if i have to achieve 16 Mhz bandwidth without doing any zero padding then I will choose the sampling rate to be 16 MS/s.
Just one last question, does 5421 AWG support only variable sampling rates like can I get precise 16 MS/s sampling rate?