Is my internet connection speed normal?

I'm curious about a few things concerning the speeds I'm getting. Let me first describe the equipment I'm using:

A desktop computer with an Intel 82579V (wired).
A laptop with an Atheros AR8131 (wired) and Atheros AR9285 (wireless).
An Asus RT-N56U router, recently upgraded with the 3.0.0.4.318 firmware.
I also have a 100 mbps connection.

I've been using Speedtest.net to check my speeds, and this is what I've seen:

Using the desktop and router I'm getting 0 ms ping and slightly more than 100 mbps downstream, which is the same as skipping the router and just connecting directly. So there's no problems here and I'm obviously happy with these speeds.

Using the laptop and a wireless connection i'm getting 5 ms ping and 40-50 mbps downstream with 802.11n. The interesting thing is that I'm pretty sure I was getting over 70 mbps when I checked a few months ago. Has the speed degraded this much with the newer firmware, or is something else wrong here?

Here's another interesting thing. Using the laptop with a direct wired connection (not via the router), I'm still getting 5 ms ping and around 70-75 mbps. Shouldn't I be getting the same speeds as my wired desktop here? Is it the Atheros AR8131 that's causing this?

I hope someone can shed some light on this, unless it's all perfectly normal and I'm just being paranoid.