Using the FTDI chip is a bit of a low-tech solution... if high speed
data transfer is important I would say use one of the normal megas which
has USB built in (eg AT90USB1287) or one of the AVR32s. Alternatively
most ARM7 chips (Atmel or NXP) have all these features and more for a
similar price to the AVR32/XMEGA, but obviously you'd need a different
development system.
--
Tim Mitchell