Speed up transfer of 145 GB to USB 2.0 drive
You could speed things up by connecting the iMac to a newer Mac in target disk mode (connected over Firewire) and then try the copy letting the new Mac do the faster copy.

However, the estimate might be over inflated and once you get over copying the small files, the actual transfer might only take 5 to 8 hours even if the Mac is running mostly idle.


http://www.wolframalpha.com/input/?i=time+to+transfer+145+GB+at+a+data+rate+of+10+megabytes+per+sec


While the transfer is running, you can see both the instantaneous transfer rate in terms of data rate and IO rate. If your data rate are low, it could be the files are small or fragmented and you actually have hit an IO rate limit or that there are hardware issues slowing down the transfer.


http://www.wolframalpha.com/input/?i=time+to+transfer+145+GB+of+data