Got cent key two or three days ago. Downloading blockchain was a big trouble, so i checked peers list, got their ip's, deleted all ip's that has lover than v10.3.5 and not maximum height then added lines to wallet config file as connect=peer_ip and after that restarted wallet. In debug.log i've seen that wallet (each time i run cent/piggybank wallet) rechecks all blocks from block #1 (but rescan=0, checkblocks=1, checklevel=0) and when height was last downloaded block (in my situation it was 840k blocks, ~a month to download) downloading of blockchain was successfully started without big delays (because of connect= lines, this says to wallet to connect only to this peers [good peers with latest wallet and correct blockchain]). A few hours and blockchain is downloaded and i send my cent's to exchange.
About importprivkey - after each importprivkey wallet program is hanged. Each time. So i enter "importprivkey KEY Name", hang, wait ~minute, kill wallet process, restart wallet, wait for working gui, import new key, hang, wait, kill and so on till all keys imported.