Then we're hearing things rather differently? I found the 325is brighter across the board. The measurements show this here:
http://graphs.headphone.com/graphCompare.php?graphType=0&graphID[]=383&graphID[]=373&scale=30
The very small differences in the 5kHz range are most likely due to measurement variations. As a result, I prefer to use the innerfidelity measurements (being an average of 5 measurements instead of one-offs like Headroom):
http://www.innerfidelity.com/images/GradoSR225i.pdf
vs.
http://www.innerfidelity.com/images/GradoSR325i.pdf
These actually show a bit more treble energy in the 5kHz ish range on the 325s. Could be HRTF differences between our ears? But most have commented that the 325s are the "brightest" in the Prestige series. They do some things very nicely like the bass and quickness, but I couldn't get over the treble.