which is why i posted my multiple of 3 strategy and personal conversion from BJ's to Sierra's all done with OEM parts.  it turns out this is going to be incredibly simple if you read carefully what i wrote.  the only ones that are going to get screwed are HF competitors b/c HF can afford to do the MPP (chips only) b/c of their smaller, more efficient chip design:

https://bitcointalk.org/index.php?topic=270384.msg2975145#msg2975145

Let's use those two numbers as bounds for the size of the silicon under the lid. If the die(s) take up just 30x30mm of the space under the lid, then:
     30x30mm = 900mm^2
     100 GHash / 900 mm^2 = 0.11 GHash/mm^2

    Or if the die takes up a bit more of the space under the lid,
      36x36mm = 1296mm^2
      100 GHash / 1296mm^2 = 0.077 GHash/mm^2

HashFast's Golden Nonce chip: I don't have to estimate the size because I work at HashFast. Smiley
   One 18x18mm die is able to do 400 GHash (nominal - more overclocked**)
   Hashing per square mm:
      18x18mm = 324mm^2
      400 GHash / 324mm^2 = 1.23 GHash/mm^2