[blykins]

They absolutely *can* take over 6000 rpm......there are no problems with doing so, other than overcoming the issues with valve float and lifter function. You can use short travel lifters and if you lighten the valvetrain enough, they will go 6500-7000 rpm. The lifters will not explode.... Barry R's last EMC entry was a 7000 rpm hydraulic roller....

Now, with that being said, a solid is more suited for higher rpms, because you can run more spring pressure to keep everything in check, without worrying about collapsing the lifter.