I would probably go with the 6x55W. It's on the low end of watts per gallon for growing live plants, but should be enough for the easy to grow, low-light plants. 8x55 would be even better if it will fit, that would get you up to 3.25w/gal
if you decide to do more live plants.
Having more fixtures gives you more freedom to adjust the light level. All 6 or 8 may be too bright for the "look" you want and may cause algae to grow very quickly. I switched to a 10w CF
bulb in my little Eclipse 5 Hex and now algae grows much faster than before, so it's just something else to consider.
If I were setting it up, I would have six or eight timers to gradually turn on the lights in the morning and off at night for a really cool sunrise and sunset effect.
The Actinic bulbs aren't necessary for FW
and really make the tank look blue with typical FW