Mouse,
I'd definately go with double ended HQI 250 watt 10,000K metal halides (whew!). They produce the greatest light intensity per watt for any metal halide bulb I know are avaiable.
I'm unfamiliar with the 13,000K bulb, since they're not readily available here in the States. However, from the reports I've read, it is a double ended HQI bulb, much like the 10,000K bulbs manufactured by Osram/Sylvania. Spectral analysis of the Osram bulb showed it radiated light close to 13,000K; this might indicate the 13,000K bulb is nothing more then a repackaged/relabelled 10,000K bulb.
If it costs more, I'd just go with the double ended 10,000K. If it's not HQI, I'd definately go with the 10,000K.
I like both the Tunze and the Sea Swirl. If buying a sea swirl, I suggest multiple 3/4" units vs a 1" unit (like mine). With the larger motor it uses, they're mildly noisy. Sea Swirls are very reliable, unlike their terrible predecessors, the Aquagate I & II. Tunze, of course, makes quality pumps. It's a shame manufacturers here in the States can't make such high performance, reliable powerheads. In other words, you can't go wrong with either.
As for {squat}, you'll know when you reach 1000 posts
It's a little (and pointless, as most things are
) "The Sump" inside reference.