I really dont know how well those things perform. I imagine they perform adequately, but not better than average. You should really have some active cooling on something that is overclocked, or immensely powerful. It is going to conduct alot of heat, you want to get it out of there, and passive just wont do it IMO.
That is the better of the passive cooling for video cards though.
The one in your syg? If it is a server, hmm, just reset the card to stock speeds. At stock the card dosent get TOO hot, and the no noise cooler will perform better than the stock one (on the card you have, anyway) so if it is running stock speeds and not too hot, you are good.
Alright, the Leadtek comes with a monstrous cooler on it, and it would be very detrimental to performance to replace that one, because you will more than likely replace it with an inferior cooler. Make the rest of your computer passive, you should still have a fan or two just to circulate air, especially in a server. An entirely passive server isnt wise man, they are always clicking away and making alot of heat.
Timmer: That cooler is very good as far as passive coolers go, dont judge it by the looks. It's only metal, cost them MUCH less than $40 to make it, I'm sure somewhere around $4 to make it.