I've been field testing with these two units in a project I'm doing for my church (discussed earlier). Of course, the DI-524 is a 54Mbps "g" router, while the DI-614 is a "b." While my tests do support that the 524 is faster, I can state unequivocally that the 524 is much, much weaker as a wireless transmitter. When used in the same area with the same antenna(s), the 524 causes my signal at one particular workstation to drop to +/- 20%, compared to +/- 45% with the 614. The measurements are via the Dlink utility.
Just an observation.