Originally Posted by Kimmo

The float is a lack of precision itself, so I wouldn't say you 'must' have a floating upper pulley. In fact, I've found it helpful to swap them when the pulley's become worn and even sloppier, or the derailer is worn and there are too many errors adding up.

I'd say no float usually means the indexing adjustment must be more precise, but also that the pulley's position will more accurately obey the shifter, which should be a good thing unless the shifter is worn or not exactly compatible.

On that note, yesterday I worked on a bike rocking 8s Campy Ergos, a Sachs-Huret RD (600 FD with alternate quicker cable routing), and 8s Shimano cassette... it was an impressive mix and match.

At work we stock replacement pulleys; we just have these cheap plastic BB jobs that come with a few sets of different plastic bits to go in the BBs to space them for various derailers. There's no float as such, but the upper pulley has thinner teeth. They work great.

Oh yeah - don't get sucked in by blingy anodised ones - unless they're plastic they're noisy as hell.