I'm always all for installing a bigger cam, but usually for the wrong reasons (mostly the lopey idle). Now, back to the real issues...
Valve float is caused by a lack of valvespring pressure (inability to hold the valve closed) nothing to do w/ lifters
Good quality hydraulic lifters should be fine at 5500 rpm. There are plenty of high hp motors running hyd cams.
The only benefit of a solid lifter is that you'll have the opportunity to check the valvetrain often because the valvecovers will be off so frequently while you adjust valve lash.
If you are itching to do a cam swap, go for a roller setup. It'll require some mods(read that as $$$) but it's money well spent