If your response is for me, 10051 is not an official release and will probably never be an .iso file.  Possibly the next official build will be a later build number.
 
You say your download speed is 6-7 MBps, is that a typo and you mean Mbps?
 
There is someone in another forum posting about long install times.  In their case it was related to language packs and they made a point if you upgraded from build 9926 the install would not suffer due to the language pack slowdown.
 
If you have a normal type install, and of course it depends on how much data has to be backed up, I would think 3-4 hours would be a maximum install period.  These builds are different in that they are downloading during the install which slows down the process.  I just discovered my 10051 install would not complete until I had an active network connection.  With no connection, the install kept rebooting and asking to supply the connection and when I did, the install completed.