Difficult to read too much into Williams' form at the moment. They haven't exactly gone for a hot lap yet and claimed that they weren't going to chase headline times at all at Jerez. Stint 3 in that simulation would have been low fuel though
since it would be towards the end of the race and it is suspected that they let the car run dry which teams often do in testing for fuel consumption analysis purposes. On the face of that assumption Senna's quickest lap was on low fuel and the slowest of the cars with exception of the Caterham although obviously we don't know if the stint 3 tyres were brand new or part worn nor which compound they were. As ever in testing more questions than answers and the few answers often produce many more questions.
They are also mixed reports from trackside observers. F1 Kate amongst others said that the car (at least in the hands of Maldonaldo) looked twitchy and "skippy" didn't hold it's line well in corners whilst the Red Bull and McLaren looked very good. Not an comprehensive evaluation as you'd expect the Red Bull and Mclaren to look planted anyway and any of their drivers would look significantly better than Maldonaldo if we're brutally honest.
Meanwhile Peter Windsor (a looooooongtime F1 journo, manager etc) said that in the fast corners the Williams looked impressive. Despite his impressive CV it's worth noting that Peter Windsor can also be a bit of a tool so I wouldn't set too much store by his impression just yet.
Craig Scarborough seemed fairly impressed with the FW34 design concepts though, yet it's worth noting that it displays essentially (from the outside at least) the same concepts as the FW33 which so impressed technical people last year and yet which spectacularly failed to deliver.
I really want the FW34 to be a good car, consistent points scorer with the off chance of a podium but I have to admit my expectations are rock bottom. Maybe I'll be pleasantly shocked but I doubt it.