SVideo is about 5 MHz and the signal is already fairly blurred right at the source ... quality cables can be surprisingly long without /noticeable/ quality loss. It's an analog signal, so with length it'll just get poorer.
DVI in turn runs up to 165 MHz signal rate. Five meters or so should be good, longer might not be a good idea. Thanks to the digital nature of the signal, there's a fairly sharp edge to overdoing it - it's either perfect picture or no picture, with a narrow edge of twinkly-twitchy not-really-a-picture inbetween, not the linear gradual quality loss you observe with analog signals.