Might be worth a little caveat on that chart. The OP is a professional pilot asking a specific question about a particular machine.
Lots of pilots read this forum though and many are in training or low hours. The reason instructors teach much lower limits is to keep them well away from the danger zone for both vortex ring and power settling.
300fpm and 30kts marks the boundary in the light helicopters in which we teach where significantly different handling characteristics begin to emerge. It is those changes that we try to instil as warnings to sort things out before problems occur.