I have a Givi E55 my wife hated the back rest pad. She prefers the extra room she has without the pad. I would never mount a heavy box on the shit factory rack it will crack. I have the Givi 410 mono key mount with reinforcement arm its pretty stout.
Check out www.tourandride.com for the best prices on Givi stuff.
I will be putting the Riders Discount Triumph 675 up for sale next week or two...let me know if anyone here or that you know of is interested. Would love to see it stay local...with a 4 year old i have no time to use so it needs to go to someone that will. Trades and or cash welcome.