"safe RPM "
I'm not familiar with the 440 Source stuff. I know who they are, but have never had any of their parts. I feel it's unfair to call it cheap junk with not having any experience with it. It could be budget parts that are very reliable.
That said, I would think 5800 to 6000 rpm would be safe assuming the rotating assembly is well balanced.
What is the RPM range for the cam?