i wouldnt call classic fast outdated
it lacks ability to log additional auxilary inputs but it is an easy to work wideband correcting system with good logging ability with a laptop and is relativel cheap for used setups compared to going to an XFI
xfi is faster and has more input capabilities (nice for logging fuel and oilpressure with a PlugNPlay kit) , with a faster processor it can log more channels , can opt for an internal logger, can doVSS , a/c idle idle up and clutch disconnect at WOT , will lock a lockup converter , boost and egr control.. and could add traction control (black box)
user interface (c-com XFI) works very similar to classic fast (c-com WP) and aside from a couple more tables and parameters using either one with CCom requires almost no relearning
if those features on XFI arent needed i would just replace the classic
if you decide to go XFI call hartline performance