UV-A ends and violet light begins at about 400nm on the spectrum chart.
http://eosweb.larc.nasa.gov/EDDOCS/W...lors.html#blue
Visible purple seems to start at about 440nm. I suppose it depends on who you are. Most actinics, or 'true actinic 03' bulbs try to peak at about 420nm. They appear dull, but that is because our eyes arent tuned in very well to see this spectrum. Only about 10% of the cones in our eyes are tuned to see the entire blue spectrum at all. Also, as the nm gets smaller, the frequency gets higher, and the energy required to produce bluer light is higher than redder light... so bulbs tend to not be as good at making blue, and of course purple.
Where violet ends and blue begins can be somewhat personal, but most blue bulbs are designed to peak at about 450-460nm.
The bulb I would suggest combining with the Giesemann 14,500K is the ATI blue+. Other mfg's do make their versions of this bulb as well... Aqua Science 22,000K, and Giesemann actinic+ are made by Narva for instance (ATI is made by Sylvania). Any one of these three bulbs should be fine for supplimenting the 14,500K megachrome... as yes, its only 'lacking' spectrum, if anything, is that it doesnt have the 'deep blue' spike of some 20,000Kish bulbs (like the pheonix 14,000K).
So Id say start with the Giesemann if you want 250's. There are plenty of people who run this bulb on its own with great results (Sanjay, for instance, on his 500g is running 400's). IF you can keep your water from getting a yellow tint, the bulb keeps its crisp white look, and its intensity will also carry farther.
Should you want a little more blue, 2-4 strips of blue+ style T5s is all you need.
Still, that adds up to the same light as just getting dual 400's with Aquaconnect 14,000Ks then... still something to consider. With the height of your tank, its something you might consider still. Sure, its 800+ watts of halide, but you have a tall tank!