I know my thread is older now but...I decided to just get the studio version..Producer was an extra $100.
To set the record straight I retained ALL my synths and FX and even V-Vocal from my Sonar 8.5 install and everything runs flawless in X3. I also should have realized that all the FX and synth installs were installable from tthe old SONAR disk if needed.
The reason I went with Studio is because I own Maschine 2.0 and Reason 7 and Native Instruments Komplete 9 Ultimate. I already have an enormous amount of FX,Synths,Refills,Samples etc. and I would have never needed the producers extras.
And as a note I tested a large project running both Reason and Maschine rewired and was only using about 25% cpu power and it all ran as smooth as silk. ;)