I have watched all 3 of the 4 day test sessions very closely, and even though you can never get a complete picture due to varying fuel loads, you can get a pretty clear picture of how much fuel people are carrying based on the length of the runs theyre doing, between refueling.
This year is looking to be closer than ever, with the front of the field massively compressed compared to the last few years. Obviously there will be teams who bring some large upgrades to Melbourne to try out in FP1, but apart from RBR who are slightly ahead of the pack, the fight for 2nd/3rd/4th/5th will be fierce.
The new parts the teams have been testing have been many and varied. McLaren have copied Mercedes front wing W-duct, a couple of the big teams have copied Saubers exhaust outlet orientation, the only thing Im certain of is no team has tried to copy anything on the Ferrari, as its tragically slow.
I would say that at this stage, based on putting together all the lap times from testing and taking into account the tyres those laps were made on, and fuel corrected, the pecking order is as follows, but it is FAR closer than last year and will only take a tiny slip up to fall down the list.
Red bull
Mclaren
Mercedes
Lotus
Ferrari
Sauber
Force India
STR
Caterham
Williams
HRT/Marussia
11 days and counting until FP1