I would leave the return pump as is and place a "Poormans Wavemaker" inside the tank itself. Increasing water flow is important but, for several reasons, it is unnecessary and inefficient to send it through the overflow and sump area. The Poormans Wavemaker is so named because it is inexpensive. It is very efficient at alternating flow. Any size Maxijet will work. The size selected depends on the size of the tank. Look at the bottom of the first post in this thread for the link that leads you to more details:
http://www.utahreefs.com/forum/forum_posts.asp?TID=9244
That thread may shed some light on other questions you might have as well.

Edited by Mark Peterson - November 18 2009 at 8:07am