Case-supplied fans tend to be the quieter, lower RPM types (cheap!) which don't shift that much air. Many aftermarket fans will be more effective.
The Vipers are quiet for what they move- and of course they'd only ramp up when needed. But, if you want to shift more air, at higher RPM they will obviously make a bit of noise, that's pretty much unavoidable. But they are only 'loud' right up near 100%.
The Arctic fans mentioned by MrPotato would be a good alternative, I only mention the Vipers as that's what I use.
Just had a look at your case... is it possible to remove the mesh grilles around the front panel? That should improve airflow a bit. Personally, I'd get the tin-snips out and have that fan guard off the back too, but that's just me... not going to recommend that too heavily...
Also try the PCI blanking plates as mentioned above. I wouldn't worry too much about dust unless the PC is in a particularly dusty location. Quick flick with a soft, dry paintbrush every couple of months should be all the cleaning needed.