Yes. Modular allows you to remove the cables you do not need. Here is a set of images of the DA850:
Note the back view doesn't have cables coming out, but just a bunch of connecions for the cables.
The best way to tell how many rails a PSU has is to go to the manufacturer's website and look at the specs. The last PSU you mentions is NOT single rail:
Look here: http://www.silverstonetek.com/produc...1000_spec.html
You see a 12V1 and a 12V2. Thus, two 12V rails for this one. Note that the max total combined load is 70A (75A peak).
Then, look at the DA850: http://www.silverstonetek.com/produc...a850_spec.html
You only see one 12V rail, delivering a max load of 70A.
Given that the DA series is better quality than the Strider (the ST1000 is a Strider), I would pick the DA850 in your case. It has all you need: plenty power, modular, and a single 12V rail.