I wouldn't call "the number you are all aiming for" staking their reputation... or even a claim.  Vague comment is vague.

Let me put it another way: is it their stated policy to replace any customer chips which won't go above 300mhz as part of the warranty?  If I bought 1,000 chips from them and tried to return the ones that wouldn't go above 300mhz would they take them back promptly for a full refund?  Has someone tried this?  These are the sorts of things to look for.  There will always be significant chip-to-chip variation; since you can't test their unsorted wafers yourself you have to rely on their public statements and returns policy (i.e. staking of reputation) to figure out what counts as "typical".