Ok this helps a lot :-) I had a feeling a USA-free itin might be in the works, which is why I did the 2nd routing. Ok CRWSTAR3 without USA. In that case I'd choose carriers with good C class and/or 2 class service to make the most of the fare (of course, if you're crediting to a specific FF program and intend to use points/certificates to upgrade (eg: LH, UA etc) that will factor in to what you do. Also if you're flying paid C you might want to consider putting into SQ PPS - if you're not already - in which case you might want to skew as much travel to SQ flying as possible).

So, I'll use those assumptions to create a CRWSTAR3 and see how we go:

MEL-SIN-NRT-ICN-HKG-xSIN-NRT-VIE-FRA-LHR-FRA-YYZ-YVR-xSIN-MEL

I'm sure others will have crafty routings that are better than mine!

notes:
3 transfers @ SIN allowed including 1 stop
MEL-SIN-NRT/SIN-NRT/YVR-SIN-MEL all SQ
(I did consider looking at some of those euro tags like AMS-MAN but I'm not sure if SQ still has any, and they were only ever a few days a week anyway, so decided to keep it somewhat simple).
NRT-VIE on OS 2 class
FRA-YYZ on AC 2 class

38698 miles @ GC

Other options worth considering:

* fly via JNB for interest sake instead of running around asia a bit
* If you can stomach it, fly BD transatlantic C class into IAD/ORD - supposed to be a great product, or at that do SQ FRA-JFK.
* substitute some of the asian flying to bounce around europe a bit more if only to try some of the "smaller" carriers: SK JK OS*
* avoid airlines with lesser C classes, widely agreed to include TG and OZ
* Alternative to NRT-VIE=NRT-CPH on SK which is also 2 class.
* Don't fly OS BKK-VIE as it's actually Lauda, and the product isn't as good in C.

Obviously you prob. don't want to just muck around visiting SIN 3 times and Narita twice. If there's any other places you can think you'd want to go (remember, you must have 3-15 stops on a Star RTW ticket) then you should think about that. Also depends which FF program you will credit to as it could affect the most optimal routing for miles/credits, etc. For example some programs are generous with minimum sector lengths (LH, UA) which you can take advantage of. Also as I said if you'd plan to upgrade any sectors, it makes sense to fly your "home" airline.

Hope this helps as a starter to work something out.