You can apply manual metric values to the various TCP/IP settings on the adapters, the lower metric number will be the default gateway (you could just as easily temporarily disable one adapter or the other for the duration of the ping test).
You can access the metrics in the properties for the adapter, highlight TCP/IP protocol and choose properties, and then choose advanced, you'll see the automatic metric enabled by default. you can
uncheck and manually set metric, which becomes the preferred path.
You can then use static route statements to route traffic to a target IP (or range) through a specific interface metric:
http://www.tech-recipes.com/rx/478/nt2000xp-add-a-temporary-route-to-the-windows-routing-table/That route can be temporary or permanent, depending on which options you choose.
I've found, for simple testing, just disabling the NIC you do not wish to use is the best way to gauge performance/etc, and if you want to choose a prefered path (probably the wired adapter in this case), just give it a lower metric number manually and it will try to use it first (and fail over to the higher metric, in this case wireless, if that fails).
