If your laptop has a N nic card then it would help to get an N router.They are all backward compatible to B and G also.
I too have Comcast and was using the same router you have.
I upgraded my speed and had to buy a SB6120 DOCSIS 3.0 modem for the speed tier I am on.
I tried using my laptop with the old Linksys router and could not get near the speed I should. My laptop has a N nic card so I bought a Netgear 3500 N router and my laptop speeds more than doubled. Not only the speed but the distance from the router has increased considerably with a 5 bar signal.
So I guess it depends on on what NIC card is in your laptop.
I don't know about the ipad wifi and how that works.
A word of caution, If you do get a N router stay away from Linksys. I had two of them before the Netgear and had to take them both back because I was having to re-boot them every day or the speed would go down to almost dial up speeds.
I have had the Netgear for 6 weeks without any problems.