Please check partition size before you try to update or like me you will have lots of grief.
1st issue for me peer to peer knocked 80% off the download speed anything I got from peers was worthless as Blizz dropped its input by a huge amount ie 100mb from Blizz would drop to 20mb yet peer gave 5mb back
2nd issue is if anything borks the download is labouriously rechecked byte by byte before the install will start again
3rd issue was down to size (it does matter ) its only 5.3gb but that grew my wow folder to around 52gb since it was only 57gb total and it was not alone it borked the install twice before my lightbulb went on
Everyone but me will know all this and more but if anyone is as dim or dimmer than me I hope it helps
Spent 24hrs doing the patch and in the process ended up buying a new virus prog moving the folder and patching several addons to versions that crash
Happily I can now log on (just buggered if I know how to play now)

Mine took yonks to update

Totally went into it blind, didnt realise about partition size, but I guess I got lucky