After some tinkering, false alarm; it was actually the software. Getting consistent 35-40MB/s now.
SABnzbd+ vs. nzbget
I used SABnzbd for about two years now, and only feeling the bottleneck with these speeds. Absolutely demoralizing to see 20mb/s when i'm paying for at least 32mb/s.
With nzbget, i'm now a happy camper