A treble booster model.
For those who don't know, a treble booster isn't an equalizer, it's the earliest form of an overdrive that mainly affected the high end, thus the name. Just about every great classic rock and early metal tone owes something to a treble booster. Notable users include Brian May, Ritchie Blackmore, Tony Iommi, David Gilmour, Jeff Beck, Clapton, Judas Priest, Marc Bolan, Rory Gallagher, etc. It's a sound that you really can't get with a normal overdrive pedal. Logic Studio actually has a halfway decent model in the Pedalboard plug called the Hi-Drive, but I'm quite sure IK could do a much better job. No one else is really doing this, and it's a sound that's as integral to 60s and 70s rock and metal tones as anything else.
I'd buy it for sure!
http://en.wikipedia.org/wiki/Treble_booster