Given the type of water in lake malawi, the 10k/actinic would be my choice. Of course, I use actinic combos on all my tanks. Just not 10k/ actinic combos. Actually, I hae a single ZooMed T8 ReefGlo (50/50 6500k/420 actinic mixed phosphor) on my 46, and I love. I have a male Jewel in their that looks fantastic under that light.
Marineland doublebringts are just bright enough to light up a 20 long. From what I have seen, you would have to spend at least 600$ to get enough LED out put for a 55.
What I would do is buy a 2x6500k T5-HO, buy a 420 actinic bulb, and keep one of the 6500ks as a spare.
Its all up to personal preferance.