For the maths.
If you use one of the inner 2 bulbs for the UVB, uvb will drop 60%.
If you use one of the two outer bulb spots, UVB will only drop 40%.
If you are only using 1 UVB and 3 6500k, id sport for the 12%/10.0 because you will be losing around half your output.
Now if your quad has 4 individual reflectors, its like having 4x the light output. With a quad with a mono reflector, 4 bulbs is only 250% brighter than 1 bulb in a single.