Is there any benefit of 315MHZ over 433MHZ?
For the average user both frequencies will work about the same. Generally the higher the frequency the easier it is to to transmit through the typical Faraday cage (re-bar in walls) but 315 and 433 are pretty close.

I would expect around 1/2 mile line of site with these using a 1/4 wave whip antenna, good ground plane, and decent code. Of course the range is farther but it is harder to get reliable data the farther you stretch it.

Here is a code example that for the simplicity is very reliable.
http://www.picbasic.co.uk/forum/showthread.php?t=12554
I would think this code will work with the modules you are looking at.