I've never gone through a fitting, just test rode many bikes, found one or two that felt right, and went from there. My last purchase (Lemond Reno), was bought after test riding many diffterent brands and styles of frames ("traditional" and "sloping top tube"). The Reno just felt right, though I did have them swap out the stem for one 10mm shorter. My mtn.bike has a short top tube (typical for older GT's I'm told), but works for me. I guess a custom fitting might be advantageous, but for me, test riding has done OK so far.