Which Cadence product are you referring to? I know a number of them run best on Opteron compared to every other platform out there. Many Cadence products are not yet officially ported to AMD64, but they are coming soon.
"Porting to the AMD Opteron processor-based systems is a natural fit for Cadence. We already have customers taping out designs with 50 to 100 million gates. Porting to AMD64 technology offers tremendous advantages to our customers who want a quicker design time, more capacity, and increased performance for their high-end chips", said Lavi Lev, Executive Vice President and General Manager of the Cadence Implementation Division.