which way should I go?

250w on a 20H?
You may need more than an ice probe to cool that baby down.

If it were my choice, I'd go with the 250w and the 55w 03 PC... it'll take some of the yellow out of the halide.

Heck, why not just put 'everything' in it...

Well, that will cut down on some of the heat transferred to the water from the air, but halides also give off 'radiant' heat which will heat the water without needing the air to do the transfer (think 'heat lamp').
It's that heat that you need to worry about.

Theoretically, the 2 4" fans if configured in a push-pull configuration (one blowing in, one blowing out) should provide more than adequate air cooling for the bulbs... it's just that darn radiation you have to contend with.

I have 80cfm of air running through my canopy on my 55g and my 250w halide still brings the tank up about a half-degree per hour... I can't imagine what the same lamp will do to a 20... I also have a 10 gallon sump that's about 2/3 full so I'm more in the range of 60 gallons of water... you'll be at about 1/3 of that amount.

HTH