Shimmy, had a plain 210 before, 2005 model I bought new. Great machine that gave me 7000 hours of relatively trouble free service. I had a 350c for 6 months last year for some larger clearing projects we had. That was my experience with the c series. Thought it was slow, and sluggish. Salesman said they were focusing to much on efficiency. He had complaints about the c models. Good machine and we liked it, just wasn't quite as snappy. Totally different machine size wise so not great for comparing.
The 210d reminds me more of my old 9010, fast and strong. The older summitomo machines where quick, and relatively strong. The d series feels very similar. The return to dig cycle is actually decievingly fast. What's really hard to get used to is how quite it is. Engine doesn't ever seem to load up, no matter what your doing.