Wipe All Data vs. Passcode - Which Should I Use?

2 Security Questions for anyone:

1. I lost an iPhone 4S, had a passcode set, and could not find it using a Find My iPhone App to wipe the phone clean. What will happen if the person who found it tries to unsuccessfully guess the password 10 times, i.e. will they ever be able to access my data even though it will not be "wiped" clean?

2. I've replaced the iPhone with a new iPhone 5S. I'm still wary of choosing the "Wipe All Data" after 10 tries because the fingerprint option is not flawless, and my typing in passwords is not flawless, either (even though I know the password off by heart, I still sometimes hit the wrong sequence when typing fast). If I back up my data in the Cloud or on a Mac, do I not have to worry about this.

Thanks for any info!