Force Series 3 90GB has maximum sequential read speeds of 550MB/s and sequential write speeds of 500MB/s. It features asynchronous flash memory.
Force Series GT 90GB boasts 555 MB/s read and 505 MB/s write speeds. Unlike Force Series 3, the Force GT comes with ONFI synchronous flash memory.
The drives are backwards compatible with SATA 2 3Gb/s and suggested retail pricing for Force Series 3 90GB is $159, whereas Force Series GT 90GB should go for $199. You can find out more on Corsair's page here.