I saw the light
Today I've lost about 6 hours to find out why POLLING DUPLEX make all my WCF services work extremely SLOW. The reason was Global.ashx. Don't know why it caused such problems, but when I've deleted it everything started working correctly.
WOW, I built a WCF Duplex app separately from my main website, I had it working perfectly, so I migrated it in. Suddenly it was dead slow. I google, found this post, deleted my global file (it didn't have any code in it, just empty subs), and it fixed the problem.
Who would have guessed? Wacky. Thanks!!!