Items in inventory, as well as item drops, greatly decrease FPS

[only latest two snapshots were listable, listed all other snapshots as 1.8]

Massive FPS drops occur the more items there are in sight, peaking with a full inventory / creative inventory.

Occuring in 14w31a, 14w30c. Likely occurs in other snapshots as well.
Reproduceable, but not constant - some users have also encountered this issue, but some others have not.