The frequency limit for bit banging is usually limited by the GPIO pins (well, their drivers) rather than the core clock. I use some ~250MHz PIC32MZ's with their GPIOs capping out at around 50MHz, and even the raspberry pi with a core clock of ~1GHz can only bit bang with its GPIOs up to ~60MHz without running into problems. As for LVDS, it takes up more area and power, and you usually need to license the IP block rather than it being available for free from the standard cell library provider.