We travel with an iPad2 wifi only and a Garmin 1350LMT. Both were bought in 2011 and, for us, were the best solution. Since no one else has responded, I'll share my obviously biased opinion FWIW. It sounds like you haven't spent any money yet, so hope some of this is useful.
I would not get a 7" tablet to use as a GPS--it compromises both functions. Our 4.3" 1350LMT was an upgrade from a 3.5" 255. The larger screen is a useful improvement, mostly because you get a QWERTY keyboard instead of ABC. For me the 4.3" is as big as I want to go even on a truck dash. Information on a GPS should be visible at a glance. IMO, the larger the screen the more you have to focus on the info in the corners and that extra eye movement is a distraction. It's been awhile since the auto industry figured out that nobody actually had to read an indicator gauge. They just have to be positioned so normal temp, press, and batt is at TDC and you can tell at a glance if anything is wrong without having to focus and concentrate on what the numerical value of any gauge is. The further a GPS moves from this model the more distracting it becomes, not to mention the blind spot it creates.
I'm a bit paranoid--theft and heat--so don't leave the GPS or iPad in the truck. Depending on what you're doing, a 7" tablet could be on the big side to carry around compared to a GPS that's only wallet sized. I'm not familiar with the Galaxy wifi, but on the iPad only the wifi+3G has a GPS receiver. I have lots of iPad specific info, but these are also questions you should ask before investing in a Galaxy (open the page and type GPS into the page search function to get past all the other stuff in these long pages):
iPad 2 FAQ
I don't want to hijack this thread. See this new topic
where I comment more on the tablet alone as an RV accessory.