GF Tass is a proven great bike (bias and generalization intended); if it fits you, its worth a shot.

for Fire mountain, if its a 2005 model, it should be a great bike. Kona did something to the Fire Mountain for 2006. as you may have noticed, Kona changed their XC line frames and gave it a more boxy look, but the fire mountain did not get this update, I dont know why. also, I think the fire mountain has a different geometry for 2006 than the rest of the pack. so, if you buy a 2006, please do some research. 2005 sould be fine, with some price reduction. best of luck