Hi there, the ASI290MC will be excellent for imaging the blue planets, and the 10" will also be the best scope (aperture always wins with planetary). The best focal ratio to use with planetary is about 5x the pixel size of the camera, so for the 290MC you will be looking around f/15.
I imaged both planets 2 nights ago from my backyard in the Melbourne suburbs (see my post
here ) using my C9.25" SCT, 2.5x PowerMate and ASI224MC camera.
The planets are small and will be in the center of the frame, so you don't need to worry about coma.
If you've never done planetary before, these tutorial videos will help.
http://planetaryimagingtutorials.com/
I'd also start with Mars, it's much bigger, and easier to frame and focus on.
Andrew
P.S. I should also point out that the preceding Neptune was one of my worst ever - there is a better version here, when it was in a much better position in the sky.
http://www.iceinspace.com.au/forum/s...d.php?t=184973