Check out their new rw line before you buy another wp. I have a wp 25 in my 30g and just added two rw-8's to replace the hydors I had on wavemaker. I was really happy with the wp until I got the rw's. It's a much better pump. I'm now considering getting a third to replace the wp...
Also, I'd consider getting a bigger return. You can always dial it back a little with a ball valve if it's too much, but most folks run a little higher volume through their sump.