Believe me, I'm more paranoid than that fact might imply! If anybody's wondering, there's no point in tracing my address and breaking in and stealing my computers. That side of things is well taken care of. The psychology of how I managed to HODL them that long is interesting and I'm not sure I understand it myself. Sure there was the temptation to buy new toys but I wanted to hold onto them until the sum was meaningful i.e. pay off the mortgage. Does that make me more or less greedy? I don't know.

I had been intending to send a raw transaction, but what I actually did was to download Bitcoin Core and then the blockchain and utterly disable the internet for that computer. I then copied my private key over onto the Bitcoin Core wallet, which is encrypted, then I just sent the 50 bitcoins to an address on my Ledger Nano. Given that the computer was not connected to the internet the transaction was not broadcast, so I get the transaction ID then used getrawtransaction through the console, then decoderawtransaction to try to verify it. I still haven't sent it.

Would it make sense to send the transaction to a testnet? I'm not sure to what extent the testnet mirrors the current blockchain?

I'm posting here for several reasons.The main one is that I don't want to make a silly mistake. The other is that I'm simply curious about what stopped this transaction working previously. There's something odd about those 50 btc. They show up happily on Blockchain but I couldn't recover them with other wallets. When I ran pywallet on the wallet they were in, it showed up the few bitcoins I had from bitcoin faucets but didn't show the 50 I knew were left from bitcoin mining. I could only see them on the bitcoin-qt wallet. I wonder, 90% in jest, whether that's what happened to all the MtGox bitcoins. Is this a well known bug?