343i has two weeks to fix some pretty big issues with Halo: Reach on PC, and if they can't, the game might not hit promised high-end performance targets.
Right now Halo: Reach on PC is locked at 60FPS for its beta testing flights. But it could stay that way when Reach launches in December, possibly even for an undetermined time after release. In a recent forum update, 343i's Tyler Davis says the team's work will carry over long after Reach's release with "more improvements beyond launch."
He also said the team still isn't happy about Reach's frame rates:
"In the current flight, we were able to further test our experimental implementation and the feature does not meet our quality expectations. From our learnings we're currently investigating and working on fundamental improvements. When we have a solution that meets our quality bar we will first flight it with the community before releasing it more broadly."