Multiple 1031's - Calculating Liability after a 2nd or 3rd

[Andrew Kensmoe]

I'm trying to decide whether or not to 1031 a property and I'm curious as to how to calculate the potential tax owed if I did not do the 1031.  (Note - I do have an email out to my CPA, but not holding my breath for a quick answer.)  The property being sold is part of a previous 1031, which is where my question lies...

Here's the scenario at a high level (using hypothetical numbers).  Also, let's disregard depreciation recapture for simplicity. 

1. Sell property A for $1,000,000.  Net proceeds are $650k.  Taxable Gain is $500k. 

2. Full 1031 into 2 properties (B and C).  Property B for $750k using $150k of the proceeds and the rest financed.   Property C is an all cash purchase of $500k using the remaining proceeds. 

3. Property B is now sold for $1,250,000.  

Question - How do I calculate how much of Property A's taxes would be owed with the sale of property C?  The simple answer is to just do a 1031 again, but I'd like to weigh our options...  Is this just a simple ratio of the purchase prices between properties B and C (750k to 500K)?  Or do we have to take into account how much of the proceeds went toward B and C? 

Thanks for any insight!