I use my N7 offline, for GPS, utilizing Nav Free, a free app on the Market.  It works great, but does take up some space.

what's the free app?

Google Map without WIFI cannot do GPS navigation. The offline map only is useful to map search when without Wifi.  For your question, the nexus 7 definitely can be a bigger GPS but need to purchase a GPS software. I bought my nexus 7 last month and purchase a GPS software named SYGIC. It works fine on my nexus 7.  One more things should be aware that GPS map data need a lot of storage space. I download US and Canada maps and it is almost 4G. Thus you'd better to buy a 16G nexus 7 if you want it be your GPS when you drive out.

Onyxluo