I believe 2900-3000 is about the max speed you can expect from a Deneb but you know there are exceptions. My 555 BE hits right about where you topped out with really good cooling and since it's basically a Deneb -2 active cores, more or less the same thing.
The Thuban based chips are the only ones you can realistically expect to go above 3000MHz with any given example. It's obvious that my NB speeds were the deal-maker for me and I was suprised when the chip ponied up and delivered with H2O used for cooling. The exact MB/RAM combo used is of course a factor too but sadly that MB I was using kicked the bucket or I'd have tried it yet again here.