  Spectral fitting of the spin a in the microquasar GRS 1915+105 estimate
values higher than a=0.98. However, there are certain doubts about this
(nearly) extremal number. Confirming a high value of a>0.9 would have
significant concequences for the theory of high-frequency quasiperiodic
oscillations (HF QPOs). Here we discuss its possible implications assuming
several commonly used orbital models of 3:2 HF QPOs. We show that the estimate
of a>0.9 is almost inconsistent with two hot-spot (relativistic precession and
tidal disruption) models and the warped disc resonance model. In contrast, we
demonstrate that the epicyclic resonance and discoseismic models assuming the
c- and g- modes are favoured. We extend our discussion to another two
microquasars that display the 3:2 HF QPOs. The frequencies of these QPOs scale
roughly inversely to the microquasar masses, and the differences in the
individual spins, such as a=0.9 compared to a=0.7, represent a generic problem
for most of the discussed geodesic 3:2 QPO models. To explain the observations
of all the three microquasars by one unique mechanism, the models would have to
accommodate very large non-geodesic corrections.
