I would suggest he 'maximum' speed quoted would be under perfect conditions. As soon as others start using the connection the speed must drop; this also applies to other conditions - the line quality, distance from your local exchange etc.
You may get an improvement using a router capable of higher speed but it is a risk you should determine. If you are happy with your current speed I should save the money.
As an aside, do you mean 7MB/sec is your usual speed. 7GB/sec would be very quick.