If you use Crower stuff, absolutely do not use there valve springs, that is my opinion.

Any aftermarket valve train should be of a higher quality than stock, or why bother using it? if it can't handle 9k rpm's it's not worth it in my book, especially for all motor setup's.

The people that I know PERSONALLY that have had Crower products fail have all used the full Crower set up, valve springs, and titanium retainers. one had crower cams the other had ctr cams. The one with crower cams snapped a cam into 4 pieces at 9k rpms, the other had a TITANIUM retainer shatter!!! causing the valve to drop into the chamber and totally fuck a motor that only had 17k miles on it, and he wasn't even driving hard when it happened, the crower stuff had only been in for like a month!

My personal thoughts that some others that have been around imports for a while agree with, the Crower valve springs are just too stiff, causing undue stress on the cams and retainers.