When I had 150W 20K XM's on my Sunpod fixture, the blue was very nice. However, I've heard that XM's don't last as long. I always tried changing out my bulbs every 6 months.
below are pics to my old tank under 150W 20K XM's.
http://picasaweb.google.com/phupharm...30792038320338
However, on my new tank, I have 150W 20k Radiums in my MH HQI. I'm not sure if it's b/c the change in ballast, fixture's simply closer, reflector, or if it's the bulb itself, but the output is better. It's probably a combination of all of the above. I haven't objectively measured it yet with a PAR meter, but, I bet it's better. However, I've noticed that my colors don't jump out as much without my actinics on.
I would try both. You'll eventually have to switch out your bulbs to maintain intensity anyways.
Hope this helps,