I'm programming a development kit which has a Virtex5, to interface with an A2D model (AD7823, Datasheet is linked).
The I/O voltage on the kit is 2.5V, where as the operation mode of the AD7823 is between 2.7v to 5.5v. I/O max switching speed is planned to be 20MHz.
Since the Virtex5 will drive the A2D and since the output of the A2D are inputs to the Virtex5, I've figured I'll need two high speed voltage regulator. One to increase the voltage from 2.5V to 3v (Chose this number sporadically of the 2.7-5.5v range) and the other to decrease the voltage from 3v to 2.5v.
There are voltage translation buffers you can use. I think TI has bus translation transceivers and they can meet your timing requirement of 20MHz easily.