I too have a very very large amount of pictures....but to keep them on my phone where they are backed is just too much.
I agree with you about the pictures thing. But the solution is simple. Don't use you iPhones native photos app to store all of them. I mean...that would make restoring to that backup take forever.
I have probably 3GB of photos, but I don't trust iCloud to back them up.
Use DropBox, or SugarSync, or SkyDrive...or like me...use all of them.
I always have all my picture easily accessible at all times on my iPhone, but I don't keep them all in my camera roll..just the ones I want there.
So instead of having your camera roll take your entire 5GB of iCloud space, upload them to one of the apps Mentioned and delete them all before backing up. That way all your photos aren't hogging all your space, but yet are still completely accessible through your iPhone.