I would like to upgrade my 4.5" f/8 Newtonian to a 6", but my storage and portability requirements make a traditional 6" f/8 unfeasible. I need some assistance in determining which of these two options are the better choice for a shorter tube:

1) The new Celeston C-150 HD - this is a short tube Newtonian with a built in secondary corrector lens and large secondary that yields an effective focal ratio of f/7 (essentially an f/3.5 with the lens doubling the ratio).

2) Celestron's older SP-C6 (also the C-6) - their Vixen-made 6" f/5 model from the 80's and 90's.

I plan to use the scope for brighter deep sky and planetary observations from an urban setting, so sharpness and contrast are considerations.

Anyone out there that has experience with either of these two scopes or can provide some expert advice on quality and suitability for my needs?