most of the freebies use lower resolution which will look crappy when enlarged,
for such a use i would spend a few bucks and get a quadrant map off USGS site.
i have one for my land and its great.
i also use the freebies for local areas, but havent made large prints of those,
you can also try saving .pdf maps off of google earth or mytopo and take it to a local print shop and see how much they charge for a large print,
my survey map which was close to 30"x20' was something like $5 for black and white