Hornsby might be better. Castle Hill has already boomed on the back of the rail project. (My sister sold her 3 bed/ 2 (or 1.5) bath /1 car (garage) townhouse at the corner of Lynstock (just across the street from the one in your link) with nice large garden for around $775k or so around April last year.) I can't remember if it was freestanding or not but it felt like it was. Not as new as the one in your link though.
Hornsby meanwhile hasn't yet really boomed but should if/when they build that missing northern link (tunnel) from M2 to M1 taking away all the traffic heading north. So if you are happy to be that far north, it should be quicker/better to get to in the future. Btw I don't think Castle Hill will ever fully get rid of their traffic issues, and the train lines from Hornsby should be better in general than Castle hill. (Although very frequent every 5 minutes, there won't be any direct train into the city. As it stands, commuters will have to change at Chatswood which is not so good for people with prams, wheelchairs, lots of luggage, disability)...