We need to be able to analyze our PPC leads' quality based on the key words used for each Marketo landing page we use for our PPC campaigns.

Out of the box, not reliably. 

If you're doing explicit campaign tagging, you can have five hidden fields on your forms, each capturing a UTM parameter. Minimum viable product is to have them caught from the URL string, and then better version is URL string->cookie->hidden fields. Then you'll have the UTM parameters (including utm_term, which is the keyword) on the lead record. 

Auto-tagging AdWords links won't be written to hidden fields this way, though, because the auto-tagged links from Google don't follow traditional utm parameter strings. 

For optimization purposes, I usually do keyword-level analytics reporting through Google Analytics and the goals you already have set up—for conversion-rate-optimization, that's mostly all you need. That's assuming your business has longer sales cycles and fewer numbers of customers. By the time I find out that "mananaging company debt transactions" led to one closed-won lead, it's mostly not actionable, especially since keywords are going to be long-tail for the most part when you're doing broad-match PPC keywords.

Cheers,
Edward Unthank
Founder
Etumos