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The trick to getting a hydraulic roller cam to go well past 7K rpm is a v-e-r-y light valve train.

1) As Rick said, beehive springs with Titanium retainers would be a good start.
(OEMs have already learned that)

2) Next you need light valves. Titanium intakes with Ferrera's hollow stem stainless intake valves would fill the bill.

3) Also, as Rick said, you'll need quality hi-rev anti-pump up hydraulic roller
lifters.

4) Another integral part of the recipie would be very light roller rockers.

If you've done all that then a hydraulic cam will rev to 7K, and well past.

Unfortunately, all this is just half of the equation. To achieve any form of longevity you need a light rotating assembly, pistons, rods and crank.

Chebby has accomplished all this in the C6 Z06, which I own. It has hi-rev lifters, bee-hive spings, titanium intake valves, hollow sodium filled exhaust valves, light forged crank, titanium rods and ultra-light Mahl cast pistons. It spins 7K easily, from the factory. With a small amount of mods, it'll go 7.5K. A lot of people are producing waaaay over 700 FWHP with these engines, in streetable trim and the engines are going 200K miles to boot.

To acomplish all this in a "dump truck motor" FE would be very expensive. To me, 6K rpm in this motor is really all I/you need. The heads, even with extensive porting, are very prohibitive to deep, hi-rev breathing. You can spin them higher, but with minimal benefit due to the head design. The LS7 heads flow 355 CFM on the intake side right from GM and with additional CNC porting they go well past 420 CFM @ 0.650" lift.

Food for thought...