You cant go wrong with Rouse Hill, Kellyville Ridge, Glenwood suburbs at this moment – looks like a steep climb is imminent with Rouse Hill being the next CBD like Parramatta in the years to come. The T_Way is doing wonders, and there is a lot of infrastructure investments given that Sydney has to grow only one way, ie West! But having said this, "Units" in Rouse Hill dont sound like a good idea. You probably need to consider a house to do better, especially with dwelling to land component being very high in the lifestyle seeking western suburbs.

Oh and one more thing, your comment about ""there appear to be very few Unit blocks in the area – therefore demand is likely to remain high- encouraging capital growth"" does not seem to fit the Economics of demand and supply.

Well in the first place, there are few Unit blocks because Demand is LOW for Units. I know one block of Units being advertised for the last 15 months atleast in Kellyville ridge, and thats the only block of Units up there!

Cheers,