CAT 40 versus CAT 50

I'm only familiar with CAT 40 machines and tool holders. How much more performance, rigidity, chatter resistance, etc. can you expect to see out of a CAT 50 machine?

I know metal removal is driven largely by spindle horsepower, so you'd expect a 25hp spindle to remove roughly the same amount of material if it's either a CAT 40 or CAT 50 (assuming it's using the right tooling for that size spindle and taking the right size cuts at the right RPM).

Is there any real benefit of a CAT 50 machine when you can get a 20,000 RPM CAT 40 machine and remove tons of metal using a 3/8" end mill and taking light high speed machining type cuts?

Thanks
Jon