The Send to Motion functionality in FCP 7 doesn't interface with Motion 5 nor do effects/filters/transition you build in Motion 5 work in 7. Basically the only thing you could do is export completed animations in 5 that you could then import into 7 but for everything else you'd stay on 4.
Noah
Call Box Training.
Featuring the
Panasonic GH2 and
Panasonic AC160/130.