The Panaracer Fire FR 2.4 is close to a Maxxis 2.7 in size when your talking about tread width. 2.7 - 2.1, big size difference don't you think?

Anyway i use 2.5 Kenda Nevegal Stick-E up front and 2.35 Maxxis Ignitor rear for DH. For XC, i just use the Ignitor's. All seems to work pretty well for me.