Here are my guesstimates:
~$2500 for 6-core (no gfx upgrade, gfx level 1)
....
Although I suspect they might dump 6-core and go with 8/10/12 options, but we'll see.
Highly doubtful. The pricing on the v2 ( Ivy Bridge) -E ( no Apple won't use these but the Xeon E5 1600 series will extremely likely have the same prices) has leaked.
http://www.anandtech.com/show/7193/intel-ivy-bridgee-pricing-leaked
The roughly equivalent to E5 1620 i7 variant , i7 4820K , is $310. If Apple previously used $294 CPUs to hit the $2500 mark it is highly unlikely they are going to use a $555 to hit the same price. Even more so in the context of dual GPUs added to the bill of materials (BOM).
The E5 1620 is likely at least $100 cheaper than any 8 core E5 2600 model they could select. It also would beat the slop out of it on base clock rate ( 3.7 GHz versus something in the mid 2 GHz range. )
The early indications are that E5 v2 prices are going to be very slightly higher than E5 v1 prices (continues long term trend for Intel). 10 and 12 cores are going to be up at least as high as the current 8's
http://www.cpu-world.com/news_2012/2012030701_Intel_rolls_out_Xeon_E5-1600_and_E5-2600_CPUs.html
If want a base clock rate anywhere near a E5 1600 then up in the upper half of that old range (i.e., > $1,500 ).
~$2500+ for 8-core, dual AMD FirePro W5000/W7000
The W5000 can't support the number of displays the Mac Pro has to, seven. There is a small chance the mainstream version is artificially crippled, but not really a "good" sign if it is.
~$3200+ for 10-core, cto, dual AMD FirePro W7000/W8000
~$3900+ for 12-core, cto, dual AMD FirePro W8000/W9000
More likely a pair of W7000 equivalents only to hit any of those prices. I'd be somewhat surprised if Apple has a 10 core option. The standard configurations will probably go 4 , 6 , 6. 12 and maybe 10 would be BTO options.
New 10 core versus old 12 core options is probably going to have lots of quirks when compare performance and price. Similarly against 20 core boxes from other vendors similar hang-ups if the customers are primarily focused on x86 cores where more of the BOM budget is spent on x86 cores than GPU ones. If the 12's are crazy high priced perhaps; just to hit a more reasonable "greater than 6 x86 cores" price point.
The 12 cores E5 2600 are probably around $2K a piece ($1,700-2,300). The W9000s would be a similar sized contribution by themselves. That will easily blow past $4K.
An "all" E5 2600 line up doesn't make much sense at all. The dual GPUs are going to drive BOM material prices up. The 2600 series only adds more to that. For a single E5 system the 1600 options are more cost effective. They are designed and priced for those kinds of systems.
Pricing is largely going to make or break this Mac Pro. If the pricing is wrong this will fail.