I guess it depends on the cost of the new processors at the time.
I agree. The current entry processor used is a W3530.
http://ark.intel.com/Product.aspx?id=41313&processor=W3530&spec-codes=SLBKR
It costs about $294. So whatever is in the Xeon E-5 range that costs $290-350 range is what they will use. That's likely to be 4 core variant.
You can look at the "pre-order" prices for the Xeon E-3 series.
http://www.cpu-world.com/news_2011/..._and_prices_for_Xeon_E3-1200_series_CPUs.html
Some of those are in the $350+ range and are at 4 cores. They may be a bit higher than the official prices but a useful gauge. So, it is very unlikely that a Xeon E-5 is going to have more than 4 cores and be lower than $400 unless severely hobbled on clockrate (GHz).
The current "entry" 5xxxx series Xeon used by Apple is the 5620 which comes in at $387 (
http://ark.intel.com/Product.aspx?id=47925&processor=E5620&spec-codes=SLBV4) but is clocked down at 2.4GHz.
I would guess something like 4 cores and about 3.1GHz base rate would get the selection from Apple. That's about a 10% jump in raw clock and the Sandy Bridge has better cache/throughput architecture. That's enough for a nice 15+% gap on a chart between "old" and "new" for Apple's website.
[and if Apple can't find a E-5 in that price range they will throw an E-3 into the mix which would practically guarantee it is 4 cores. ]
The E-5 are currently rumored to have between 2-8 cores.
http://en.wikipedia.org/wiki/Sandy_Bridge_(microarchitecture)#Server_processors
I don't think 2 core will cut it even though it will probably be cheaper (it likely will be gimped in some way). I think the lower end E-5's and mid-upper end E-3's will overlap in price because aimed at different targets but with similar performance numbers (at least on mundane apps. E-5 will have bigger caches.) However it is a fallacy to think that just because 8 core models show up in the new line up that the prices on 6 core models are going to crater. Perhaps they will drop some, but not enough to drop to "entry level" prices.