G'Day Marcus,
Yep, I've got that exact combo on my boat, both great units.
Pics of the 107 in action can be seen on pages 12 & 13 of the sounder reading thread on top of this page. I use it for Bay work as well as offshore jobbies too. We've had it working fine at over 220ft off the Gold Coast.
The 3500 is a relatively new addition, but since I've owned and used Lowrance before, I'm used to their menu systems and went with the 3500. The Nav card seems to give better detail (IMHO) and is far superior than the old hand held that I had previously.
Traveled from Reddy Bay to Russell Is onto Peel, all in the dark using the 3500 as a AID, and found it extremely easy to navigate the channels round there.
You won't disappointed.
Cheers,
Tony #