Sadly Intel is to be blamed for hot CPUs for which you need a good thermal system, which usually means louder fans. Use a headphone, thank me later.
Helios 300 has one of the best thermals in a 15.6" laptop right now. Moreover, it pushes 55W to CPU in turbo mode vs Intel's 45W TDP or 35W set by some manufacturers. Maybe that's why higher load on Helios, or case of a better-binned CPU in Y540 resulting in similar performance for lower voltage. Need much more data to give a conclusion.
Check Jarrod Tech's reviews & comparison.