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Hi Goran
I've recently gone through the same upgrade thought processes, and love to image galaxies. I've moved up from 600mm (ED80) at f/7.5 (with a DSLR) to 1600mm at f/8 (RC8) (with an Atik314L+). I've also got a fairly cheap Lightwave 0.6x reducer (Altair Astro), which shows no sign of coma at the corners of the small Atik chip (not too bad either on a DSLR chip)/ This reducer works well with my Atik314L+ on an ED80 and also on the RC8. It gives me fast f ratios (about f/4.5) at 360mm and 960mm and handy FOVs for nebulae with the small Atik chip.
I think a Powermate x 2 on an 8'' newt should work fine, I almost went for this option - it kind of gets you an RC8 anyway. Oversampling is about right at 1600mm with the Atik314. Of course, with a powermate x 2, your f ratio will drop from f/4 to f/8. Per pixel, you will have only one quarter of the light. However, you would gain about 6-7 times as much sensitivity on the Atik314 vs DSLR when doing hi-res luminosity subs (no Bayer filter, and bigger pixels).
Only nusiance factor at is getting the right spacers/filter wheel widths to match the required back-focus distance on a reducer.
Sam
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