When I recently migrated my Late-2009 iMac to my new one I connected the machines by ethernet cable and used the Migration Assistant. You don't need a hub, switch or router, just an ethernet cable. I have about 500GB and it took about 2 hours tops.
I connected my 2009 iMac to my new iMac via Thunderbolt/Firewire Adapter Cable and it took 3.5 hours to transfer 450GB. I had thousands of small music files though.
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As stated above I put my 2009 iMac Core 2 Duo in target mode and used a Thunderbolt/Firewire Adaptor cable to do the migration. Both Macs were using Mavericks.
I was thrilled with the results. iTunes files came through perfectly and I had some problem files... they came through with the same problems which I have fixed.
I did have a few things to do. I had to fix a broken alias link... fortunately I only had one. I had to manually tell Time Machine where my backup files were, but it then connected without a problem. I have a Menu Item Program which did not load. I haven't looked for it because I have a program that does the same thing better anyway.
I want to give you my impressions of the late 2013 iMac.
It is really fast. I have the 1TB SSD Pcie and the 780 with 4mb. The Blackmagic Speed test gives read and write speeds over 700. Programs load instantaneously or almost so. I use my Firewire drives and even though the faster Thunderbolt connection does not make them faster, the fact that they are reading from my SSD makes them very fast. I do a manual incremental backup of my huge iTunes folder which used to take 120+ seconds and now usually takes about 15-30 seconds. Perhaps there was something wrong with the connection to my old Mac which made it slower than it should have been. But in any case the speedup is delightful.
The sound card has been greatly improved over the 2009 sound card. Music is clearer and it is much easier to tell the difference between lossless and lossy files.
The video is amazing. I don't use the iTunes visualizer hardly at all but I had to check it out with the new video card as a test. Wow. No stutters quick transitions even when the screen is in full screen and the visualizer is filling the screen with many different colors. Amazing. My internet pages load much quicker with the new graphics card. It is like going to a faster internet connection.
I am very pleased with this computer.