I was thinking that if I use 800x600 resolution, then the signal frequency is 40 Mhz, and if I use 640x480, the frequency is 25 mhz.
The frequency of the signal is the same for VGA signal or TTL or LVDS...the only difference is how this signal is transmitted.
For VGA and LVDS, R G and B signals have different levels, LVDS uses twisted pairs and differential signal so it is very safe. VGA uses small coaxial wires, one per color.
For TTL, it is one wire per bit, on or off.
It seems to me that TTL should be even more resistant to noise and cable length problems than VGA because TTL signal is stronger and binary. If we have 1 or more meter VGA cables we should have 1 meter or more TTL cable?
SCSI III cables transmit a 40 Mhz signal (exactly the frequency required by 800x600 SVGA) using 34 shielded twisted pairs.
Using such cable, it is even possible to put each TTL wire in a separate shielded twisted pair.
I am not used at all to cables and signals.... do you see a reason why extending TTL LCD cable this way should not work?