Max SB RPM?

The biggest factor in how high the engine will spin is how well the valve springs control the valves, valve float and cam design.
Of course, crap bottom ends will spin that high, but for how long.
Example of this , is a freind who had a stroker 340 to *I think it was* 392 cubes. It would spin that high all day. Big roller cam in a W-2 engine. Valve springs wore out a bit and power went down. Replaced springs, power cam right back.