Apparently great minds think alike, because I've been researching this topic over the last few days. Unfortunately, I may have reached an even more expensive solution. If a 1D4 sells for $2,000 USD on ebay, and I can sell my 5D3 for $2,500, why not just put the money from the sale of the 5D3 toward a 1DX
Scenario A) If I keep the 5D3 and buy at 1D4, I'm out $2,000 total.
Scenario B) If I put the $2,500 from the sale of the 5D3 toward a $6,000 1DX, then I'm out $3,500 total.
The price difference between each scenario is $1,500, which isn't exactly insignificant, but we're approaching the end of the year and I could use a big tax write-off
I have a buddy approaching a million clicks on his 5D2 that's in the market for a 5D3, so I wouldn't even have to monkey around with ebay