My reasoning behind this is that: when it get's near the end of downloading the blockchain it uses a ton of CPU and takes days to finish....
That has nothing to do with your wallet.dat and everything to do with the makeup of the blockchain (thanks to SatoshiDICE which started on stong at about 95% of the blockchain).
So, ... unless your wallet.dat is corrupt or something, that is not your problem.
As far as it re-downloading the blockchain, I'm not sure why that would be doing that.
Also, if you are on an encrypted filesystem that will really slow you down for blockchain downloads.
As far as a client, such as Electrum or MultiBit, yes, the key(s) can be exported. The wallet formats are different. You can import private keys into electrum I believe.
Personally, I use Blockchain.info for my daily wallet as that is accessible via web and mobile app. It is a hybrid EWallet, doesn't have access to your private keys.
But that too would require that you export your keys and transfer them. Letting the client complete the download is probably your safest point forward, then send a payment to empty your wallet rather than importing keys.