For quite some time I've done the 4-day and 5-day splits which have worked quite well but I think I've been over-training as a result.
I've changed to an 8-day split so I'm training the same body part every 8 days:
Sun - rest
Mon - chest (for example)
Tue - train
Wed - train
Thu - rest
Fri - train
Sat - train
Sun - train
Mon - rest
Tue - chest (repeat after 8 days)
I've found that I'm gradually getting my energy and enthusiasm back and it's working pretty well for me. I'm more endomorph than mesomorph (60%/40% endo I'd say) by the way.
What do the group think about the split? Is this too much recovery time? Is it acceptable to making good gains or good for cutting up? Or is it a waste of time?
Proteins are good... Fats are good... Carbs are the problem!
You will ultimately encounter the effects of "disuse", training every eights days, especially bodyparts such as upper back, arms, ones that recover relatively quickly will result in loss of size and strength.
It sounds like you need to make some changes if you've reached a state of over training. Maybe just a one or two week break from training. Or, a change in your work-outs, e.g. stop going to failure for 4-6 weeks, or cycle your work-outs, heavy one week, light the next, things like that.