A few quick facts, then speculation....
AMD has stated, on the record, that barcelona is a rework of the existing k8 pipeline. Some heavy modifications to be sure, the 128 bit single clock cycle SSE execution units being the biggest one. In ~~theory~~ this will give Barcelona a big floating point edge on Conroe which is also 128 bits wide, but can only dispatch a single 128 bit SSE instruction per clock versus two for Barcelona.
But as a rework, there just simply are not going to be large clock speed jumps, indeed, the switch to the aforementioned 128 bit sse engines will make is tough to hold existing clock speeds, they may get a bit of a speed bump from the new (at least to AMD) 65 nano process, but well into the 3 ghz range just ain't gonna happen.
Intel will continue to lead in integer performance, there is nothing published anywhere I can find that's going to give Barcelona a bump on integer applications.
Barcelona will, generally speaking, issue 4 instructions per clock cycle,(kinda 5 under some limited conditions) versus 4 for Conroe (also ~~kinda~~ 5 under some limited situations) -The two designs have the same size of instruction buffers and issue restructions, so clock for clock, these chips will be darn close, Barcelona a tad better on FP, Conroe a tad better on Integer code.
Clock speed is pure speculation.
We know Conroes typically get to 3.3 ghz or so with ease., close to 4 on really good cooling.
~~assuming~~ Penryn has leakage issues solved to the degree Intel claims, 4.0+ ghz is not an irrational assumption, but it is still an asumption.
The other issue is yields.
If Conroe/Clovertown can hold the fort with a 3.4-3.6 ghz part on a 1600 mhz FSB, I think Intel holds of Penryn till yields are mature. IF Intel needs it for PR value, I am sureat least a few 45 nano parts can be dragged into the 3rd quarter...
The reality is VOLUME shipments of 45 nano start in Christmas 2007 - You can pullin a design, but due to change over or masks, tools, process, wafer composition, etc, logistically it's damn hard to pull in the timelines on a FAB changeover - these things take time.