I've just read interview with Kubica. He said, they'll have new diffuser and some minor tweaks like new winglets. I know, that diffuser is quite important and may come with new floor of which Kubica simply didn't want to mention, but still I hardly can imagine that will be all of those 40% mentioned several times if they are serious.
What's more, he said, new wing didn't work well in Barcelona and that he wish it will play well with new parts.
He also said, that they were very quick in Jerez - somewhere in between top 4, but they were left behind in Barcelona as they didn't bring many new parts there and new front wing was disappointing.
It looks like they will probably have troubles with getting into Q3 and just play in midfield.
EDIT: My 50th post