your "ping" or network latency relies heavily on your network adapter, router and modem. since you are using all of the same hardware with a different OS, I'm willing to bet it's the Win7 driver for your adapter... even if it's hard-wired. you may also need to configure your IP and network settings manually or download a different driver for LAN devices.
also, you may want to check background services for network activity since it's a different operating system. a certain service or process could be affecting your network connection... possibly and update service or a web plugin. if you're using an anti-virus program that updates itself, check the settings and maybe change to manual updating.