Why not go with a RW-4 instead? They seem like better pumps.
I had a WP40, and it was huge. I pulled it out and sold it, and have been running with just my MP40. I have been thinking about adding a RW-8, but haven't gotten around to ordering one.
+1 I have two RW 8's in my 150 and they MOVE water! I really like how wide the flow in these pumps is. I bought mine from fragfreaks.com, they had better deals then amazon at that time. Great customer service too.
I have a similar size frag tank, running 1 wp25 and a mp10. I prefer my mp's, but the wp25 moves much more water. If considering wp's I would think 2 of the 25's would be more than enough, have no experience with the rw's.