When I switched to an ISP with local peering, ping times between my home and my server downtown dropped to a few milliseconds. It's like being on my LAN.
If this is still an issue for AT&T, traceroute+reverse DNS of each router may indicate it.
This poor peering isn't directly a throughput problem, but really increases the chance of being routed through a congested link, which you could sometimes guestimate from ping times and peeringdb.