It was slow and crashed a lot when it used Direct3d Retained mode. 6.0 was re-written to use Direct3d Immediate mode. The program is more stable and the geometry data is exposed to program. Many of the features are a lot faster than in 5.7a but the feature set has a minimalistic philosophy. Like with the implimentation of sub-division surfaces for example. It's a straight catmull-clark surface routine which is fine but some of the more powerful programs on the market use a modified rational catmull-clark surface that allows per face/ per vertex/ per point weighting. So the nuances that you can acheive in the program are limiting you from being more expressive.
As a first time modeling program, 3dc is not a bad choice. Also, the developer Richard is active in working with his users. I've gotten him to add my fair share of features just by saying, I'd love if 3dc could do this!