i have switched from an older c2d 3.06 to the new i5 2.7 model, was this actually a smart choice? I’m running cubase 5, and a small size project is using 30% cpu on the new i5, which I recall similar size projects were doing about the same on the older one 
Choice of computer comes down to what you want to be able to do with it.
The Imacs are using SB i5 chips, but there are many differences between the different i5 variants. I have yet to see the benchmarks from the new imac systems, but I suspect the i5’s would be similar to workstations of 18months (or more) ago.
The imacs are great systems, and I know professionals using them (in particular, a number of sound editors for film) - but without actually running specific DAW benchmarks on these new systems, or knowing how your projects acted on the previous model, I wouldn’t be jumping in straight away.
There are just SO many variables with DAW usage. I’m personally having 4 new slaves built as new sample based libraries do not run well on my current system. The software uses more and more resources - and your own ability in the program may increase, and you may push it to its limits more than you may have in the past. Without a concrete way to eliminate these variables, one just cannot be sure what you need.
I personally would love SB to release a suite of benchmarks that can be used by the public, and have an UPDATED list of performance based on constant user testing. The benchmarks would relate to use in different environments… tracking/mixing (plugs), composition (VSTi’s), etc. But I think that is perhaps a pipe dream.
Having said all this, I do love the way cubase/nuendo runs on the new i7 mac laptops. With 16GB of memory installed (can be done) these are quite a portable workstation.
YMMV.
Brendan.