But, if migrating from FCP7, FCPx is so different with no guarantee that Apple won’t pull the plug again, that you would be short sighted not to look at some of the alternatives:
Avid (long in tooth, poor effects but should be around for a long time as it is their core product)
PPro (hold back from latest version though as lots of issues reported)
are the top two in order of popularity. followed by..
FCPx (tied to osx and limited development – but cheap!)
Then, also worth a look:
Vegas (tied to windows, also very different from FCP7 but has its fans)
Edius
Lightworks (editing only)
Resolve (early days)