You're probably right Mike. Where shall I move it...?
I know, I'll put it here.
I've done several long distance multi day rides over the past few years, and they always leave me wanted to do more.
The C2C is very good but probably isn't long or tough enough to sustain a five day ride even if you are carrying a lot of gear.
You could always incorporate a there and back approach by using the Rievers route, Hadrian's Cycleway or the Walney to Wear Cycleway.
I've done a variation on the Tim Woodcock Coast to Coast which took four days and the terrain was much more challenging. We carried all our stuff but stayed in YHAs or B&Bs to keep weight down.
Also cycle toured/camped in France and Switzerland which is so much better than trying to do the same in the UK. Better roads, better attitudes, better campsites, etc, etc.
I'd love to do something similar in Scotland. The attraction of wild camping and bothies is a strong one.
One piece of advice I will give is to choose your riding companions wisely. There is nothing worse than listening someone complaining every day because the route is too hilly, it's raining, they didn't sleep, their bike is creaking and they need a poo.