awells wrote: was wondering if I could get away with my synthetic quilt (+4c) at this time of the year
In Feb temperatures rarely get below 0 deg in the area. Lowest Feb temperature on record in the region is -4 (at Lake St Clair National Park; not sure where exactly) and -1.9 degrees at Waldheim/Cradle Valley (this was only from 10 years of collected data though). Decile 1 miminum temperature at Waldeim is 3 degrees, thus you can say that 90 percent of the time in Feb the minimum temp is over 3 degrees. If you were comfortable down to -2 with your quilt then you should be right as long as you have shelter (these temps ignore windchill); may just mean a night or two less comfortable than with the winter bag. These temps are all from bom website. My experience in the area is that I am mostly too hot in in -2 (comfort rating) bag and have never been too cold, but I am a warm sleeper.
awells wrote:I'd also like to carry just my 2 person silnylon fly (500g) rather than carry a Tarptent (1kg).
Many people (myself NOT included) don't carry tents at all - they rely on huts. With the booking/payment system you would have to be unlucky to not fit into a hut, even if it means sleeping on the floor (doesn't help if you get caught in a snowstorm halfway between huts though), thus the tent/tarp could be seen as a safety item in case you get caught in bad weather away from a hut. Personally though I prefer to sleep in a tent (warmer and more private than a hut). I have never used a fly on its own, so I'm making some assumptions here but I'd guess that its pretty uncomfortable in really high winds which can occur any time of year. But then if this happens just go into the hut. Also that it has no/little bug protection - in warm weather (very likely) there will be moths and midges etc out in force so could get uncomfortable - but again, you can just go into the hut. I guess it just comes down to how desperately you want to stay out of the huts.
Dave.