Depending on your cooling setup also, you might consider laying something thick and sound absorbing over that top vent. I stopped using that top vent eventually and have it covered with some Acoustipack.
One more thing, I would recommend taping up the ventilation holes on the rear of the psu chamber. This will force the airflow to come from the front of the case (and not get pulled back in) and also pass over the HD's (assuming you put them in the lower chamber). Remove the Antec fan if it's down there and just let the PSU fan do the work. A couple of hard drives as the only source of heat for the PSU incoming air shouldn't do to much to the temp.
The P180 is definitely not magic....but it does offer a lot of variety for making a wide range of systems quiet.
One last thing...the Dell, do you keep that at work, and if so would you say your work environment is louder than at home?
...Okay...this is really the last thing...20 years!
edit: the VF900 would probably be better for that card.