My vote is, run the powerfilter in conjunction with an Undergravel Filter. Put the powerfilter intake in the intake tube of the UGF.
Having that much flow cuts down on the amount of "gunk" that forms underneath the UGF since it's going to get sucked up by the powerfilter. Doing this will also reduce the load on your powerfilter a bit. Don't forget to gravel vacuum (it's important for any tank), and your filtration will be just fine.
heh, doing this in my tank gets some pretty good results (for a 55 gallon tank). I've had snails that got under the UGF plates get sucked up to and stuck on the powerfilter intake.