The issues is, while it does well comparatively at 4k, it appears to have significantly more frame rate variation. While the averages are high - they stutter more & suffer more drops (this may be a result of either immature drivers or the 4gb memory).
Dropping 2fps from the average for a much smoother experience is worth it & at it stands today the stock Ti is more stable.
Also, looking at the card temps - even thought the CPU remains cool, much of the rest of the card is pushing very high heat, this may be the reason for the slight 'under-clock', with not enough thought put into the ancillary cooling.
This is at this stage speculation, but it would make sense as to why the card is clocked so low it doesn't even reach any significant temps at all (when if it was able to easily over-clock by a huge margin it would come pre-clocked higher to do better on the first reviews).