I would do four clusters of:
5x XM-L @ 3A (like you are running)
20x Rebel ES Royals (440nm) @ 1A
4x HVTV 420nm @ 500mA (Milad's new one that isn't out yet)
4x Ocean Coral White @ 500mA
So your total # of LEDs would be:
20x XM-L @ $6.89/ea = $137.80
80x Rebel ES Royals @ $3.49/ea = 279.20
16x HVTV @ ~$13.50/ea = $216
16x OCW @ $6.88/ea = $110.08
Total forward voltages (for figuring out driver number):
3.35v x 20 = 67v
3.1v x 80 = 248v
11.1v x 16 = 177.6v
8.6v x 16 = 137.6v
Number of buckpucks needed @ 24v:
3x for white @ 3A
11x for royals @ 1A
8x for HVTV @ 500ma
8x for OCW @ 500ma
Need 24v power supplies that equal to 28A, so say 8A each, so four PSUs.
I'm at work or else I'd come up with an Illustrator design for it all.
The whites at 3A combined with the HVTV will give you incredible PAR over the entire tank, even on the sandbed. The 440nm royals would give you the purple cast you want, along with putting out quite a bit more light than an XT-E. Using the larger HVTV and OCW for exotics would reduce complexity, too, which is a wonderful thing in a build this size.
As for water movement, dual MP40s may be enough, especially if you keep them going full-blast (maybe long pulse?) and make a circular flow in the tank. Where in the tank are you planning on keeping SPS?