It depends on the altitude.
The higher you fly, the smaller the airspeed amount is.
This is the easiest source for guidance on approach / landing speeds: All Aircraft Takeoff and Landing Profiles (Version 20.1 Wiki!)
If you search for “landing profiles” you will also find more comprehensive articles for most of the aircraft in the sim.
Of course, GS is TAS without wind.
My impression is that aircraft performance specs for marketing (maybe just turboprops?) emphasize TAS rather than IAS (because progress over the ground is what has economic performance meaning for operators of the aircraft).
But pilots fly by IAS (dynamic pressure speed), and for jet aircraft also Mach speed.
The Mach speed is TAS as a fraction of the speed of sound (where the speed of sound varies somewhat with altitude and temperature).
The optimal cruise Mach number varies based on multiple factors, including the optimal underlying indicated airspeed (IAS) for the angle of attack (AoA) targeting the best possible lift-to-drag (L/D) ratio, in balance with the optimal engine performance. And the above varies with load, and density altitude etc.
So many variables to balance, no wonder FMS are crucial to modern aviation.
But I think it’s fair to say a recommended mach cruise speed, even though it is a TAS, has to be anchored to optimization of the corresponding IAS as well (due to dynamic pressure aerodynamics considered separately from the transonic aerodynamic limits).
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I think I’m the only one who flies at Mach 0.90, on the B777 and DC-10F.
Yes, but as you mention FL270…