RPMs, valvetrain weight, and valve spring pressures all come in to play. If you're running high rpms or heavy valves, the springs must be up to the task of controlling them. Since you have to do springs for the VVT 3 lifts, just make sure the springs you choose can also handle the heavy valves and any rpm expectations you have.
I spoke with Mast Motorsports last week. Their tech director told me that they have turned their ly6 to 7100 rpm, with no problems. I am cam shopping, but whatever I purchase, it will be in kit form...cam, springs, retainers, etc.
Thank you interesting info from Mast. The LY6 has Inconnel exhaust valves that can take extreme high heat. I have a GM LY6 summary that states that the engine was developed and tested for 200k miles under high load conditions.
I will if I can find the PDF online or I will scan and post it.