I for sure would go with 2 of them. You may find the 425's a bit weak, I have 2 in my 20g and it doesnt move alot of water. I also have one in my 29g cube and am not thrilled with it there. Always better to get a little extra flow than not enough in my opinion.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.