Hi Simon,
Yes, low read noise cameras produce good results with short subs. If you have a high read noise camera then, all other things being equal, you'll need to take longer subs to get the same result in the same total time.
As Glen mentioned, there are low noise cameras CMOS like the ASI1600 that work well for short subs.
Noise doesn't generally fill up pixels. Most forms of noise we deal with are a statistical uncertainty, not unwanted photons. It's sometimes helpful to think of unwanted signal as something separate to noise. For example, sky glow is unwanted signal. It's not actually noise, though it does have shot noise associated with it.
Most of the cameras we use these days are anti-blooming. That means that overflow from a pixel is gated away and doesn't overflow into neighbouring pixels.
As to what is a long exposure that's somewhat subjective. For me, 1800 seconds is as long as I normally go. I have done 1 hour subs a few times.
It is possible to determine the ideal sub length for your specific set up and skies. Shiraz wrote a nice post about one way to do it:
http://www.iceinspace.com.au/forum/s...d.php?t=117010
Cheers,
Rick.