G.Skill 2 X F2-8000CL5D-4GBPQ on 780i

[Cronos]

A little speculation.
There is (are) some chipset primary latency timing(s), similar to Intel's performance level (tRD). On Intel platform, you have direct control over this timing in BIOS as well as with Memset utility, on NVIdia, there seems to be no way you can control it.

Sadly, NVidia does not publish the datasheets for their chipsets as Intel does.

Over 1480 this chipset timing jumps to higher value. This also may explain why you cannot boot in 1460-1480 region - the timing is too tight already for this speed.