Okay here are my thoughts:
* The McLaren is relatively light on it's tyres and was struggling to get temperature into them in the cold conditions.
* So far they've only really been concentrating on reliability and basic setup.
* At the next test we'll see a new front wing and possibly snow plough specifically designed for the side pods.
* At the next test we'll see a revised aero solution around the rear, tightening the bodywork as the definitive exhaust solution is fitted.
* We'll also see a couple of trick aero devices or concepts.
* Diffuser and rear wing will receive minor tweaks.
* If the next test is cold then they'll appear closer to the pace but still a little behind Ferrari and Red Bull.
* If the next test is warm then they'll be right at the sharp end.
All just personal opinion and speculation