I sometimes ride with a group that is much faster than me. Usually, I just hang on for dear life and hope I don't cramp up or bonk. They only really smoke me on the county line sprints, but luckily they regroup very slowly after those. Some of the guys are really nice and will give me a push now and then or drop back and help me catch back on if I'm struggling. Riding with them makes me push myself harder than I think I can. It has made me faster. It keeps getting easier to keep up with them, and they notice. If they're good guys, they will help you out when they see you are really putting in the effort. I'm sure there was a time when they were between pace groups. Maybe don't ride with them every time. Do the easier ride sometimes and the hammerfest sometimes. Try to make friends with them, and if they still don't want you there, then find a new group. If you are dropping back by 5 minutes, you should just drop back to the slower group. If you're constantly opening a gap, then you are probably not ready for this group either. If you can hang on most of the time but struggle on some hills or with some really fast surges, then you probably ought to be there, but you will need a little help sometimes. Riding solo is a good way to work on the mental aspect of suffering, but if you really want to get faster, you need to try to hang with people who are faster. It is, in my experience, the most effective way. However, they need to be just fast enough that you have a chance. They force you to put in efforts that you may not think you can do solo. If you can fight for the right wheel, you can get the benefit of a good draft that will help you save some energy over the course of the ride. If you're always way off the back, then you are really just training alone.