The mmc speed is a bit limited in spec, but fanoush has a kernel overclocking the mmc controller.

The wlan chip is on the SPI bus and seems to be limited to somewhere around 4-8 as you've noticed. i have a vague memory seeing some experimental code speeding it up, but I think it was for 770 and has probably bitrotted severely at this point. Atleast file transfers over usb seem to be a great deal faster, so usbnet is probably faster too, though I haven't tried it.