Overfiltration is never a bad thing. However if your fish cant excape from the current, block the output with a large rocks or peice of driftwood to tame it down.
If 1 filter breaks, its nice to know you have another for backup.
Fish all seem happy and the current is not too bad IMO. I also had kind of a dead spot in one corner and this seemed to solve that too.
Basically, I got a 304 for about $50 - compared to about $150 for a new 305. After I finally got tired of the Aquatech, I got the new tank brackets that come with the 305 for around $20.
I like the idea of having enough filtration in each one that things will be OK if one of the filters ever quits. My next buy will be a 120g or 180g, and it will be nice to have an established filter to add to that setup.