Pre '05 would be a possibility.
I was in the shop doing a side by side comparison between an '06 X-Caliber and an '03 X-Caliber. For some reason, GF made the chainstays longer and the BB is higher. There was a gusset added at the head tube - downtube junction and there were small tabs welded where the chainstays meet the BB. I guess that is to cope with the longer chainstays?
The '06 frame was really nice though despite having those changes and being disc-only. The tubing manipulation looks to be superior to the '03 which has no variation in diameter along its tubes. The '06 also had curved seatstays + chainstays as well as more material removed from the dropouts.
But I'm under the impression that GF was marketing the 29" concept as a race bike before and now it is being marketed as a trail bike. That's somewhat confusing for someone like me who is considering a 29 for a race bike.
The only thing about the pre '05 is the BB might be a bit low. I'm on 175 mm cranks right now but being 6' 3" with an inseam of around 35", I should be going up to at least 180 mm. My friend is on 195 mm cranks, same inseam.