Hi David,
Here is a link for Ethernet performance: http://processors.wiki.ti.com/index.php/AM335x-PSP_04.06.00.08_Features_and_Performance_Guide#Performance_and_Benchmarks_2
If used in synchronous burst mode GPMC can go up to 100MHz clock frequency. It will also depend on FPGA capabilities. More information about GPMC can be found in the AM335X Technical Reference Manual, Rev. J section 7.1.
The LCD interface is dedicated. MMC Linux driver currently supports 4-bit mode only. MMC performance can be seen