when the oscillator's frequency is high,the cpu's speed is high,you can choose you oscillator's frequency as you need. usually I us 12MHz and 11.0502MHz. IF the frequency is too high,AT89S52 will be less stable.
there's a lot when you are selecting the frequency
when the frequency increases,the speed of the system also will increase
byt will increase the power consumption
so select your crystal according to the requirement.
0 to 24 MHz, look the datasheet, some atmel IC can run with 33 MHz but it's not secure
Added after 7 minutes:
11.0592MHz is bether to have a bether baudrate, it's more exact when you use 9600 bps or similar, you can get exactly this value of bps, with 12MHz you can get some % of error but you can comunicate.