Guys,
Just my tuppence worth here.
I have toured Europe almost every year for the last 25 on sports bikes (Blades, Milles, R1's, GSXr's etc) and on touring bikes (Pan, FJR, BMW RT, BMW Adventure) so I have a little experience.
1st the obvious one Touring Bikes are designed for it so are better at it....doh...and not much help.
2nd People always take way far to much stuff......fact...look at the pictures above.
3rd On sports bike if Touring with 2 people the best luggage system I found was the Ventura system. Simple waterproof and expandable and trust me 1 bag can hold enough for 2 people for 2 weeks. (Not camping ofc)
Trust me I tried panniers and different bag systems but found that the Ventura was best and didn't look to bad.
4th On sports bike if Touring alone the Ventura system is also fantastic and can use a 2nd bag sitting on the rear seat (kinda goes against the taking to much stuff statement tho but some guys will need their hair dryers i suppose) however a waterproof holdall / bag bungied to the rear seat is every bit as effective.
It's also handy to have some storage up front for items you will need to reach....passport, toll cash, toll tickets, camera etc.
Hope this helps someone
Regards
D