Do you know what the 720 gives you over the 710.No. I'll leave that to you. But I think the 720 will cost you quite a bit more, so whatever additional features it offers would have to be pretty important to you to justify the difference.
does it make sense for me to go with MRX 5 series ?Possibly yes, but it also has less power so that may be an important consideration as I know Aerial speakers generally require a good amount of power to get the most out of them. I also don't know if the 5 uses the same room correction software as the 7, so that may be a consideration too.