My wife and I like the outdoors, enjoy walking/hiking but are not into skiing or snorkeling. Taking into consideration weather [not too hot/cold] and crowds [room to sleep/eat/breathe], which would be the best time of year to spend 6-8 weeks downunder: Feb-Apr or Sep-Nov or other?

I think mid-late Autumn (April-May) is a good option because the weather's usually more settled than in Spring. With the exception of mid winter and high summer, we have a pretty temperate climate in most places. And even then, if you are coming from the Northern Hemisphere, you're unlikely to find it too cold.

Crowds are not usually much of an issue in Australia unless you're in a theme park or other venue popular with children in school holidays, and in the times you mention there are only two School holidays. These are roughly 1-19 April, 24 Sept - 11 Oct.

You don't say where you want to go. Please also note that the GBR IS NOT ONLY SNORKLING AND DIVING so that would be a "must do". At least in both countries skiing will either not have started or have finished going by your dates unless you take into consideration Heli Skiing so that is not a concern.

NZ would be great in Feb=April. March would be nice, cooled off a bit, some less wind. Later on some areas have lovely autumn colors such as around Arrowtown.

Although October is rhodie season!

Thanks one and all. Autumn it is. Will start on the SI in March and move on to Australia from the NI.

Just echoing ivenotbeeneverywhere's comment: The Cairns & FNQ (Far North Queensland) area has so much to recommend it that even if you didn't so much as take a glass bottom boat trip over some of the reef, I think it would be a great pity not to include it as you have the luxury of a little more time than many. Don't forget the opportunity of taking night trips with an experienced guide to see our nocturnal animals, too.

Autumn's a good bet, esp second half of March to early May - but note school hols, Easter and Anzac Day. Spring's not a bad option of course, but weather can be more unpredictable, hay fever can be a problem and sometimes there are lingering winter illnesses...