Reference to passengers not noticing the difference between a 310 to 320 speed decent versus a path descent on a cost index of 11 (circa 250 kts.) is not true. The noise level at the higher speeds is noticeably higher and pitch angle is quite lower (about - 2 1/2 degrees) versus a virtually level nose attitude with a calmer rate of descent.
Also, the cabin crew will appreciate that slower rate of descent when negotiating those galley carts up and down the aisles during stowage for landing. Ever experience a galley cart slamming into the cockpit door? I witnessed it whilst sitting the back of the jet during a high speed descent. Luckily the galley cart went straight for the cockpit door and did not careen into any of the sponsors who make our paychecks possible.
Anyway at the end of the day is a two minute savings in flight time really worth the effort of causing discomfort and a possible difficult working environment for those behind the cockpit?
As I get paid by the minute, I have no great need to push my jet to it’s designed limits… that’s what the test pilots get paid for. Anyway… food for thought.