not really sure, at least not right now as i can barely see the screen
. my understanding is that anything over say 3m will start to result in signal loss on an analogue monitor cable although it shouldn't be particularly noticeable. i know that my primary school had a projector permanently linked to a PC via about 6-8m of VGA cable and while the signal didn't seem quite perfect i was probably the only person who could tell.
Talking about extension....will a 15ft DVI cable between the monitor and case, decrease anything performance or signal wise?
should be no signal loss as long as the signal can overcome resistive power losses. in other words theoretically you could send a DVI signal around the world if you liked but you would require repeaters to reproduce the output intermittently along the line otherwise the power lost would result in the signal not making it.