Double ended is said to be more 'powerful' as it is fired up from both ends, and it is said to provide a more 'even and consistent' specturm. It is so intense untill needs UV-shield glass to cover it, or something along that line.
Personally, I would go for DE, but I need 400W, and they only come in SE.
Only plus I can think about SE is the convenience of it. Just unscrew it out, throw away, screw new one in. I am using Spider reflectors.
Lights combinations are up to you. Some prefer that way, some prefer this way.
I personally would suggest 2 X 150W with 10K or maybe the new BLV 14K. Whack in 2 T5s Blue for your dawn and dusk effect.
Anyway, tubes come in standard wattages and mostly in even numbers if I am not wrong.
Then again, it could be that this old man is out of touch with technology.
Is there 400W DE yet?