Please consider my company's Mongoose family of products. Each version uses full-speed USB 2.0 (12mbps) provided on-chip by a 32-bit ARM microprocessor. No crappy serial converter chips. If you want speed at a low cost, this is the interface for you.
It comes with a DLL (J2534) if you want to develop your own software. Feel free to email, call the office, or post here if you have any questions.