What do you want a GPS for? The Venture is primarily aimed at the orienteering market; the 72 is a sort of upmarket backup mainly aimed at the marine market - for instance you can connect it to an external antenna, but at the end of the day its just a GPS - it won't accept charts so its not a plotter.
The GPS 111 Plus is mainly for in-car navigation.
If you need the GPS for your RIB the handhelds have a very small display, and eat batteries. In the interests of safety you may be better off with a basic fixed unit like the 126 or 128. If you want charts you could try the 162.
As i said it depends on what you want it for. If you come across a unit that gives you in-car navigation plus marine chartplotter capability for small money let me know........
If you need more info on Garmin go onto their site and send them an email - they are usually quite helpful.