you can push it to 4ghz on air (running hot hot hot!), but probably not with a zalman 9700. those are designed more for looks than for cooling.
your best bet for air cooling is the thermaltake big typhoon ... or the arctic freezer xtreme. i've tried the zalman heatsink you're using and its performance isn't that impressive. the big typhoon is the best out of all the coolers ive tried from off-brands to flashy zalmans (yes including the one you have) to huge thermalright heatsinks.
i haven't tried the freezer xtreme though, but it looks very balanced out. also, i've bought other products (mostly video card coolers) from them and my video card is currently overclocked and vmodded running no hotter than 26.5 degrees celsius at a full load.
you should be able to hit 3.8ghz stable with the right motherboard/ram/cpu cooler combo. that is, with a bit of an overvolt.
oh, and also try using arctic cooling's MX-2 thermal compound. i tried it out recently only to find that its extremely easy to install and it flattens out better than arctic silver ever did. it's good stuff.
