Sorry to keep this away from the original topic but there is some good info here.
ATCO's, perhaps you could PM me with some actual stats next time the low TAS scenario presents itself.
The only time I can imagine a low TAS being the norm is if a ECON cruise is planned at low level (approx FL 280) or below due to strong headwinds up at altitude.
To quote some figures from a B737-700 performance manual at LRC (long range cruise), (which is slightly faster than ECON most of the time).
At an average of 60 tons the following applies,
FL 310 Mach 0.721 / TAS 429
FL 330 Mach 0.751 / TAS 437
FL 350 Mach 0.765 / TAS 441
FL 370 Mach 0.779 / TAS 447
FL 390 Mack 0.790 / TAS 453
In a 800 series a/c a 65 ton average would be applied so the speeds would be slightly higher. (These figures are based on short sectors. Longer sectors would have considerably higher weights and therefore higher speeds).
It would be nice if we were all singing from the same hymn sheet to enable a more pro-active assessment of traffic processing.