The following website is a good source of information although wading through all the details can be exhausting. I am a Holly Springs expert and very familiar with tuscany and the surrounding neighborhoods. Next time you are in town I would be happy to sit down with you and go over all the maps for future 540 and help you decide the best area to settle in. I also grew up in Charlotte so I know the pros and cons of both areas. I would love to be of service! Good Luck!
The NC Turnpike Authority is building that stretch of 540, with construction starting now (contracts were awarded last week I believe, so they are in land acquisition phase) and completion sometime in 2012 according to their website.
The section you are inquiring about is known as the Western Wake Freeway. You can find info on 540 at:
Checking the county GIS maps, the NC Dept of Transportation does own some land surrounding Tuscany. You should hire a Realtor to act as you Buyer's Agent, and they can do the research to help determine where 540 will be in relation to the houses you are looking at.
Please let me know if I can be further assistance.