In reply to Whoiskun:
Thanks for all the tips. Sadly Tete Rouse and even Nid d'aigle is fully booked for months, so no where to sleep en-route.
Further planning means that starting we start from Col de Voza or Bionnassay means a hike of around 2500m ascent, with most of the walking in the snow at this time of the year.
Will need to get to Gouter by 5pm to check-in, so that means if leaving at 7am, it will give us 10 hours for the journey. Possible, but still quite daunting.
It also means a 2am departure the next morning for a push to summit, then all the way back again.
Hopefully there will be last minute cancellations at refuges that will allow us to spend extra night, which will greatly help.