I guess I have to ask: What do you mean by groin pain? There are a bunch of different structures there, and different stuff can be going on depending on what the pain is.
If it's the feeling of numbness/tingling - like when a limb falls asleep, it may mean a number of things: Saddle too narrow. Saddle too soft and "conforming". Saddle too low relative to bars, putting too much weight on the perineum. It can also mean that not enough of your weight is being supported by your legs. In general, but especially on a long ride, you don't want to sit with your weight primarily on the saddle - you should be supported by your legs and, to a lesser extent, your arms (though too much of that causes pain in the wrists, etc). It's also a good idea, if you're experiencing numbness, to get up out of the saddle every minute or so, to give the area a break.
If you mean a pain more like bruising around the genitals or feeling like you just got kicked in the nuts, that could mean saddle too high relative to handlebars, saddle pointed too far up, saddle too far back (so you're sliding forward and riding on the nose).
I just bought a second-hand bike that had one of the Terry saddles with a big cutout in it. I know opinions on these things are mixed, but considering that the bike gives a pretty upright ride (which means more weight on the saddle), I can't believe how comfortable that saddle is, even for rides of two hours. You may be a good candidate for a saddle with a cutout...