It depends.....
If you ride by yourself, on a long ride you tend to get into the same power output level and the road bike just gives you more speed and distance. The effort is the same but the ride results are different.
If you ride with others and try to keep up with the same riders, then the slower bike will become more work. You are more conscious of keeping the same speed because of the other riders.
If you ride a slower bike like a mountain bike with others you will have more work but be the slowest one in the group. It's frustrating. If you get a nice light fast fixed gear or single speed bike you will work harder than others, but you may be the fastest one in the group. So it's a lot more fun. You eventually end up droping everyone else on the hills as you get stronger. That's much better.....
