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Looking good so far.
Ignoring all the good things about your shot like composition and colour, and just addressing your noise question:
(1) The noise level is perhaps not too grim for 3 hours with your kit. (This huge rant doesn't mean I think your image is especially noisy.)
(2) Twelve hours would halve the noise. Most of Trish's and my shots are at least that long. We've thrown up to 50 hours at the Helix for example. But it is diminishing returns.
(3) Consider longer subs. This greatly reduces noise and actually reduces effort! With an EQ6, a not so huge focal length, and off-axis guiding, you should easily be able to manage half an hour. (I used to manage 1 hour with an EQ6 and a 10"). That would get three times as much signal past the read-out transistors for each dose of read-out noise. The disadvantages of longer subs are: satellite trails, aircraft, cosmic ray hits, wind buffet, all more likely but harder to reject with a small stack, and field rotation can be a problem. If you don't have an off-axis guider, forget it.
(Tips for practicing really long subs: Choose a still night without wind buffet or risk of intermittent cloud. When doing polar alignment, get the polar axis as close as you can to the right latitude, but a tiny half-skerrick west of the pole. If you do the opposite: exactly south but say too high, you will get both nasty field rotation and your guiding will suffer from hunting in the dec axis gears backlash.)
(4) Another long shot possible thing to keep in mind is that putting the three galaxies (for very best of reasons!) right in the corners of the image is that they will be getting vignetted. You could look at your flats. A wild guess is that the vignetting will only be trivial, say 10-20% and it doesn't matter. But if it was 50%, then it would be working against you.
(5) Stating the obvious, be at the darkest site you can, with no haze, no moon glow, and image high in the sky. Photographing below say 15 degrees will usually only make the image worse because of sky glow. Bit tricky with Leo.
(6) Run the camera as cold as you can down to say -30C. After that it doesn't matter so much. Autumn is upon us. Every 6 degrees will halve the dark current, and since the noise is Poisson, the dark current noise should halve too.
(7) Advanced technique that I quite like: Take some unbinned shots (you've already done that bit) to get the bright sharp detail. Then on another night take some 2x2 binned shots to get the faintest regions with less detail but much less noise. Combine the two using a suitable mask to take the bright detail from the binned shot, the faint stuff from the binned shot, and pro rata in-between. You can make the mask from a blurred copy of the image.
Best, Mike.
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