Xilinx GTP_DUAL: wizard or code ?

I am using for the first time a Xilinx RocketIO module (I have years of FPGA experience though); normally I prefer to explicitly write on my code all the instatiations. Manual UG196 says:" The RocketIO GTP Transceiver Wizard is the preferred tool to generate a wrapper to instantiate a GTP_DUAL primitive."

Any experience and advice about coding vs wizard in the case of RocketIO ?

My application requires to use the GTP for a simple but non-standard protocol (8b/10b with a custom packet).

Regards,

Tullio Grassi Fermilab