Reply 20 of 31, by Scali
As far as I know, officially there are no 8088 or V20 CPUs that are rated higher than 10 MHz.
The fastest 'common' variation of turbo XTs is 9.54 MHz (double that of the original PC).
I do vaguely recall however that there were some 'factory-overclocked' XT clones of 12 or 12.5 MHz. But I can't name any brands or models, so I may be mistaken.
Apparently this might be such a board: https://th99.bl4ckb0x.de/m/A-B/32279.htm