Imac advice

Do you mean professional audio work?

I assume the 5400 rpm drive is offered since it is fairly easy to find cheap slow drives for notebooks (small form factor & low heat), and Apple is trying to cram all the components into an over sized video monitor case. You are basically buying a laptop that sits on the desk. The slow drive does seem to be the Achilles' heel of the machines, especially since there is apparently only one drive, and it is none too big. Most power users running Sonar use two or three 7200 rpm drives to shift the access burden (1.OS and programs, 2. audio data (projects) recording and playback, 3. sample libraries that stream from disk if applicable). Demanding projects may well suffer from the drive limitation. 

If you are planning to use Sonar as your primary software, it would make more sense to get a Windows machine it the first place, rather than booting into Windows via bootcamp. If that is your choice, you need to figure in the cost of Windows OS as well.  I would not pay 300.00 more (is that US dollars?) for the slightly faster CPU or the video card difference. But then I built my last Windows DAW for about 600.00 total including a monitor,and it makes these Apple machine's specs look ridiculous. The Apple tax you pay is not just the 25-50% profit Apple expects, but limitations in expandability.