Spectral fitting of the spin a \equiv cJ / GM ^ { 2 } 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 .