Well, what chips these are is kind of irrelevent since regardless of Santa Rosa or Montevina, the CPUs are still Penryn and are architecturally identical. The only CPU difference between Santa Rosa and Montevina performance-wise is the 1066MHz FSB. So a special 1066MHz FSB Penryn on a Santa Rosa platform is just as good as a "true" 1066MHz Penryn on the Montevina platform. Montevina would have also supported DDR3, but would have also added DDR2 800, so again Santa Rosa with DDR2 800 support is pretty close to Montevina. The newer chipset in the Montevina might have a few more optimizations, but chipsets rarely lead to big performance differentiation so a 1066MHz Santa Rosa iMac is not really a big loss.
In terms of Quad-Core, there will be a mobile Extreme Edition Quad Core for the Montevina platform. It'll only run at 2.53GHz though, so other than media intensive tasks, a 3.06GHz dual core will likely be faster. If you are going to wait for the quad core though, you'll likely be waiting a while since Apple won't be refreshing to Montevina soon, if this revision is indeed Santa Rosa based. If the iMac is indeed Montevina already, then they may decide to add the quad core Extreme Edition as a BTO option when it's launched.
The thing is Montevina consists of 3 elements, CPU, Chipset and wi-fi adapter. Apple is usign Atheros Wi-Fi, so Intel's interpretation is out of the question for now.
Yes these chips are given to Apple exclusively. They are "Penryn" core with 1066Mhz FSB and 6MB of L2-cache along the entire line ( Remember that 800Mhz first batch of Penryn processors had some entry level chips with 3MB L2, i.e. entry level MB)
Montevina has Intel's PM45 Mobile chipset, capable of supporting 667/800Mhz DDR2 and 800/1066Mhz DDR3. thinking that even DDR3-DIMMs are way too expensive and offer no significant performance, Apple decided to go with fastest DDR2 support that PM45 is yet to give, 800Mhz SO-DIMMs.
This means that xx45 Chipset is out. The only quastion is whether GMA X4500 on the embedded version of this chipset (GM45) is ready or not. Considering the rumors of design changes in MB line, MB will get this new GMA with it's design change. (And after this, all Mac line will be HD ready, and there will be nothing to stop Apple to start offering BDR Drives, except the HDCP support on the ancient ACD line)
So, Montevina is here, iMac was the first to get it, Hopefully with the introduction of X4500, Mac Mini and Macbook will get it with brand new designs... Lets not forget MBP, too.
P.S. AFAIK, Montevina's Extreme edition offering is the 3.06Ghz version. There will be no quad-core Mobile processor in Montevina, but there will be one in Calpella, which is due Q1-2009, with the introdution of Nehalem Architecture.