you cant really use HP as a yard stick for determing if a part will survive. there are alot of variables & differant ways to make HP.
RPM is critical, generally under 5500 RPMS your safe with stock internals. add a good set of rod bolts & you can go a little more.
A set of light weight pistons will take some strain off the stock crank & make it survive longer yet.
a machinist I know & trust prefers cast cranks over steel in applications below 6500 RPMs because cast cranks are generally lighter than steel (unless you buy a nice piece). He suggests a good set of light pistons & good rod bolts in the stock rods, & good machine work.