I've used PCI slot fans and found them to be very good for removing hot air from around the graphics card ! If I read the link correctly however, the Spectrum fan card is more about blowing air directly at and around your graphics card ! But under the circumstances, is no bad thing when you are overclocking !
I don't use any type of PCI slot card at the moment, just because I have 2 fans sucking in at front, 1 fan sucking in at side over CPU and 5900 card, and 2 fans blowing out at the rear ! And I suppose you could also say a PSU with 3 temp controlled fans also blowing some air out at rear ! But as it is a quiet stealth PSU, I don't really expect it to contribute much to case cooling ?
At the moment, I only have commercial filters on the two front fans, which are not that efficient ----> too much air loss for filtration given ! Maybe I'll need to try your pantyhose technique on my front and side mounted fans ? And if we are grading pantyhose, then what denier grade are you using ? Or do you just use any you find lying around ? lol