John, We are a small company just starting an ASIC design group. We had Cadence in a couple of days ago and I must say that they caught our ear with Ambit. I've been an Ambit salesperson from the early days and am no longer with Cadence. With DC 99XX, SNPS has closed this gap and both tools are about on par with each other.
Ambit holds an edge with it's higher capacity and built-in static timing engine.
When designers benchmarked the two tools, we traditionally won. Stratum One, Maverick Networks, Monterey Design, Amber Networks, etc. We had a tougher time with established SNPS accounts. The main reason was switching costs. They'll get great technology, support and much better price.