The interesting line in the X logs are:
(II) NV(0): Not using mode "1600x1200-60" (exceeds panel dimensions)
Created attachment 190481 [details]
I'm seeing the same with F8t2 (also with a Dell 2007FP). I didn't previously see
the problem with FC7 as I use Nvidia's driver; trying with nv shows the problem
there as well.
I tried FC6 with an ATI card that used the VESA driver and it showed the same
result. X is pretty much unusable in this graphics mode.
Assuming this is about the nv driver, this is a known (long-standing) bug with
no easy fix. Closing as duplicate.
*** This bug has been marked as a duplicate of 234824 ***
This bug is not limited to NV, it also occurs with the ATI and VESA drivers.