2006 was the last year with Cosworth in F1. The Williams team had Cosworth power before they switched to Toyota in 2007.

The irony about that was that the Cosworth engine was widely regarded as the best and most powerfull F1 engine of the 2006 season. It was also the first to rev to 20000RPM (both on the dyno and in real race conditions). But financial backing was vital to Williams and when the Toyota engine came at a lower price they had to switch fro financial reasons (Williams could have other reasons as well obviously).

I visited at Cosworths facilities when they developed the V8 F1 engine that Williams used in 2006. I saw it on the dyno and even then they were talking about very high revs and were very confident about the performance of the engine.