Sherman Racing Products ...check these guys out.
You can spin your stock hyd roller lifters well past 7000rpm with titanium retainers, valves, and locks... just look at what the NMRA and FFW Renegade guys are doing (do more research, lol) with stock lifters coupled with the Ti and other lightweight components. LaRocca spins 'em to 8800rpm, for example.
I have spun my stockers to 7000rpm with Manley race-flow valves (steel) and Ti locks and retainers without missing a beat. I ran the modified SRP lifters all last year (so I wouldn't have to wonder if the internals of the lifters were going to spew all over the lifter valley), shifting @ 7k, and crossing the 1320' @ 7200rpm. I am putting together a Renegade legal combo, however, and will have to put the stockers back in...
Anderson Ford also sells Hi-rev hyd. roller cams that utilize stock lifters, FYI.
One thing that is nice about the hyd. roller lifters, is that you don't have to set them as frequently as you would a solid roller setup