Well, that's another personal decision.. 'worth it' and 'settle' are hard to quantify.
I was in the same boat myself, and just ordered the 50L this morning. I did that, for me, because of the very unique look that lens seems to provide (at least in the sample thread) @ 1.2. That being said, many have commented that it can be finicky, and take some time to get used to shooting with it. For some people, traveling may not be the best time to get used to a new lens like that.. for others, it may be the perfect time.
On the other hand, I picked up the 85 1.8, and not the 85L II, because I thought the 85 1.8 was a solid performer, at much less cost, and much less weight. I also knew I'd get the 50L, and use that for any low-light needs where 1.2 would come in handy.
Putting all that aside, and putting myself in your shoes, I would get the 50L and take it with me. I would use the travel time to use it and see if it works for me, and then if I didn't like it, sell it when I returned. The market may be a bit different in Australia, but in general, I see 50L's range from $1,000-$1,200 USD used, so you'd be getting back ~90% of your money. Assuming your trip is more than a week or two, it's actually cheaper than the rental fee.
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