[popcornmix]

The overscan_* numbers are meant to be positive...

Really? I had to set mine to:
left 30
right 30
top -13
bottom -14
to eliminate overscan.

Okay, they do need to be positive.
By default for CEA (TV) modes they get increased by 32 for SD and by 48 for HD.
By default for DMT (monitor) modes they don't get increased.

You can disable the increase with disable_overscan=1.
So if you want less overscan than default, I'd suggest:

Code:

disable_overscan=1
overscan_left=78
overscan_right 78
overscan_top=35
overscan_bottom=34

which avoids the negative numbers which could cause problems if connected to a DMT moditor.