UPDATE: On this PDF (page 18) it talks about how to set the baud rates. I think it defaults to "normal" serial baud rates but there's a way to modify the baud rate choices. At least that's how it reads to me.
The CP2102 - CP2104 will do 250k; the CP2101 will not. Also, the CP2102 and CP2103 have a fixed table of rates (one of which is 250k) while the CP2104 can do arbitrary rates (within reason, see section 6.1 for details: http://www.silabs.com/Support%20Documents/TechnicalDocs/cp21...).
USB 2.0 compliant, full-speed (12 Mbps)
No external crystal required
Up to 1024 Bytes of EEPROM or OTP ROM
User-programmable custom Baud rates
Supports all modem interface signals
Baud Rates: up to 2 Mbps
Industrial temperature –40 to +85 °C
Datasheet:
http://www.silabs.com/Support%20Documents/TechnicalDocs/CP21...
UPDATE: On this PDF (page 18) it talks about how to set the baud rates. I think it defaults to "normal" serial baud rates but there's a way to modify the baud rate choices. At least that's how it reads to me.
http://www.silabs.com/Support%20Documents/TechnicalDocs/AN14...