synplify pro premier
Synplify is the bare bones version. Synplify Pro has a much nicer interface and offers a bunch of addtional features. There is a big difference between these two versions.
As I think you may have already discovered, the only difference between the Pro and Premier verisons is the physical synthesis option, otherwise the two versions are identical.
Physical synthesis supposedly allows you to meet timing on designs where the traditional synthesis -> place & route process aren't sufficient. In physical synthesis there is some iteration between the synthesis and place & route processes. Timing info from the place and route tool is fed back into the synthesis which can then try to improve the synthesis before another place and route iteration is attempted.
While this approach can give you great results with ASICs, I'm not convinced it's worth the extra money for FPGAs where I think the improvement is only going to be minimal. I think the last time I talked to a Synplicity rep the difference in cost between the pro and premier versions was substantial.
Radix