I regularly torture myself by riding with a group of hothead boys. Sometimes, they help me out if I'm lagging. Sometimes, they don't. Either way, so long as I can keep my cool, it makes me a stronger cyclist. There would be no way I could learn to hang on to a paceline going 28mph if I didn't train with them. However, I cannot do that every ride. Not just physically, but mentally. There are days where I need to do tempo or ride with the ladies or even ride solo. If I'm not feeling it, I cannot keep chasing down egotistical guys. It's miserable. Doing it fairly frequently the past year or so has made it a lot easier to keep up on a majority of the hills. I am also no longer the slowest a lot of the time, so while I may still get dropped, it's a little easier not being the only one getting dropped.

You need to figure out your food and fluids intake. You need to do some training that makes you happy. But if you have goals of improving drastically to one day be able to keep up with a group like this (my goal is to be a stronger racer, for example), then sometimes you also need to HTFU. Getting furious is totally understandable. If you do these kinds of ultra-challenging group rides, the suffering level is high.

This is from the perspective of someone who races and who enjoys the company of the guys (and so I would like to make riding with them more enjoyable). This kind of training is totally not necessary for making it through things like the MS150.