Be very wary of signing for Infinity UNLESS you are assured that your line will be 'improved'. As mixture says, it is all about the length of your line, regardless of where you live. A long 'ropey' pole supported line will not deliver Infinity speeds.
Nor will the same long ropey length underground, it's the distance from the cabinet that is the deciding factor with infinity, the final cable can be replaced with new and it wont matter which it is.