Doing a little reading I see that it would be good to use a wallet that doesn't download the entire block chain. Are you using electrum? Can I transfer over to it with my .dat file?
What would be best is if you setup Electrum and then sent to your new address from the Bitcoin-QT client. Note that the Bitcoin-QT wallet does NOT need to be sync'd to send coins. It will submit the transfer to the network even without the blockchain in sync.
A big advantage of the Electrum wallet is that it is 100% deterministic. Print out the words it gives you when you create the wallet and store them in a safe place (or 10) and you never have to worry about backups again. The wallet and all the transactions can always be recreated with those words.
For the seed what I did was installed TrueCrypt or similar and created a 10MB encrypted virtual drive file. Put all your wallets, keys, seed text, etc. in there with a really strong passphrase and then email it to yourself or throw it up on Google Drive and MicroSoft's OneDrive.