I do not think Dan's references contradict. GD will be above ICAO max holding only in high altitudes where difference GD <> Vls is quite small (say 5 kts - speaking A320). So there is not much room to go below GD and that leaves slats (conf 1) as the only option.
On the other hand, at 60 tonnes the G/D would be 205 kts, asked to fly 190 ? No problems if above Vls as per the book.
Why? Because the question is, with OEI, flaps /slats locked at zero, what speed would you fly ? VLS cf 4 + 45 kts + 5 = 180 kts, so one-ninety when slowing down on both engines and flaps available is really not a big deal.
Then 185 is S speed - optimal for flaps 1. When asked to fly 180 - no need for clean conf when optimal is conf 1. Fly 160 to OM on conf 1? Again, no problemo (provided you can slow her down that is) because it is still well above Vls and Vapp conf 1 is the precise 160!
Well done airbus.
FD.
Forgot to add: Flying one one engine would have me feeling uncomfortable, no doubt. Furthermore, I do not see reason to go 20+ knots below anything when there's more flaps available, however there is no reason to feel uneasy either. We fly Vls +15 at cruise if required, we fly Vls + 5 on every approach. Flying Vls + 20 should be no scare even if it is below optimum speed for the given conf. I like the approach speed similarity, noticed it on pprune. Normal operation Vls+5, so I will go as far as, say Vls +10 if deemed feasible.