What challenges are you facing exactly? The MSSurface is not a desktop PC, so blazing performance was not a concept they went after on their portable tablet.
Plus DWG file sizes and where you store them/how you connect to them come into play for slow performance too.

You are also comparing an old 2.6GHz processor with a much faster 3.8ghz processor and way more room, of course you will see a difference.

Are you intending to run the MAC version of AutoCAD on that imac27?
Or are you wishing to run WindowsOS on it then AutoCAD for Windows?

For that kind of money, why not purchase a true WindowsOS Desktop Workstation instead?