3. sync on a fast machine and copy chaindata directory to your slow machine The chaindata is portable across architectures. So, sync, stop the node cleanly, transfer the chaindata directory (replacing your old one), and start the node on another machine. To minimize risk, use identical versions of geth on both machines. (I did this for x86_64 -> armv7h successfully with Geth 1.4.5, others did tooothers did too.)
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