The direct exhaust is nice in theory, but yields no real benefit in praxis. I remember when the first Silencers for 9700/9800 PROs were released people reported no noticealbe difference in case/CPU temps, I don't think much has changed since then. GPUs are running somewhat hotter, but if the benefit wasn't measurable back then, then it's very likely marginal at best with more recent cards.
But I think you'll be happy with the Zalman, everything from Zalman I've had in my hands was quality stuff, maybe not always the very best there is, but certainly very good.
I got a 8800GTS coming in, let's see how much of a difference that is in overall noise compared to my passive X800XL (R.I.P.)^^