The EE Prodigy 30 would be an excellent quilt for the Southern Highlands, especially for trips with some precipitation. It will also combine well with other gear you have/may have to create a modular sleep system that should cover any conditions expected other than severe cold, say below 0F.
I use a system quite similar to what I'm proposing for all conditions encountered in the SE. The components in my system are as follows: MYOG Climashield XP5.0 quilt, Marmot Hydrogen down bag, down clothing layers, synthetic puffy layers. I can combine these in a number of configurations to handle the expected conditions. The synthetic quilt is key for a couple of reasons:
1) When used over my bag it shifts the condensation point from inside the down bag to either inside the synthetic quilt or between the two. This allows me to preserve the integrity of the down as regards moisture accumulation. This comes into play in temps below 20F.
2) I use the quilt combined with my synthetic puffies for what seems to be the most common winter conditions for us: mixed precipitation and temps between 25F and 35F. Down gets really hard to manage in such conditions, thus I often go out with only synthetic layers. Articles and forum threads here concerning shoulder season conditions are an excellent resource; what folks in the Rockies call "shoulder season" conditions is what our winters are like.
3) I use the quilt as my sole insulation on warmer weather trips. Up to about 45F I'll carry along an insulated jacket, above that just the quilt. This, combined with good raingear and a good shelter, allow me to hike worry-free on long wet trips, without worrying about taking sun-breaks to dry gear or stopping early enough to build a fire to dry gear.
There are a couple of drawbacks to my system. It is definitely heavier and bulkier than a single bag/quilt solution. You may need a bigger pack, not sure what your using. It is also more complex and "fiddly"; I can appreciate the simplicity and elegance of a single bag/quilt solution.
I say go for the quilt, the only question to me is whether to get the 40F or the 30F. The 40F might be more versatile for you, it will definitely be lighter and more compact. Enlightened Equipment makes great gear, so no worries on that front.