Fishes could care less what light is used so long as it's not too bright.
Would go with custom T8 fixture unless I was going to make the tank planted,high energy,CO2 injected at some point.(More light mean's more CO2,more nutrient's)
Otherwise, the higher lighting that T5 bulb's produce will possibly be too much light for low energy ,non CO2 injected tank and all manner of algae and lot's of it, could be result's without raising the light fixture,decreasing the lighting period,running half the bulb's,or all of the above.
For cichlid tank where keeping plant's can become problematic,,I would just use the T8 bulb's.
Even low tech planted tank, could be lit plenty for low light to moderate light plant's and no CO2 is needed for these to run well with relatively low maint.
Even those running high energy tank's ,seldom use all of their lighting without siesta's, modification's,and more than a few use little more than minimum to achieve the growth they desire.
If lighting is for fishes sake,,then it don't take much.
Would not worry bout trying T5
