I really enjoyed the choice of tempos. For example the theme and first 2 variations: Tchaikovsky wanted them played in the same tempo. Play too fast, and the opening sounds inconsequential and while the semiquavers work at a fast speed, you can’t always hear them. Start too slow, then the next two variations have to inevitably speed up to compensate, and by halftime it can all sound a bit fragmented. Gueller and Bogdanović kept the tempo-balances ideal, and by the time the first slow movement arrived, you realised with surprise that a third of the piece was done already, in the blink of an eye.