Any tools that are worth their weight in gold will be those that typically balance out the elements of optimising a page and reflect this in the grade it offers. Such as SEOmoz for example, their tools aren't going to advise to optimise everything as much as possible to the extent it is over-done, if this looks the case, then the grade is highly unlikely to be an A.
I think the term over-optimisation is largely misperceived. Delivering a well structured, compliant and semantically coded, unique website which provides original content, caters for its intended audience and takes into consideration usability measured via onsite behavior is naturally going to perform well anyhow. There are hundreds of factors granted, but generally only need to be addressed once (such as templating, internal linkage structure, URL formatting and content hierarchy) (with the website elements that is) - after this, as long as content is researched, offers value and is what people want to see, then the grade of any given page will be pretty good whilst not 'over-optimised'.
Any cheap and basic web based tool that basically just gives a grade based on title, metadata, keyword frequency, blog, social profiles is close to useless (take Hubspots free website grader for example) anyhow and wouldn't contain a formula to distinguish between whether (for example) a page has more than 500 words on a page or whether the same keyword appears 450 times within that same 500 words.
If you can rely on any set of tools online that are in touch with the latest algorithm updates from Google then SEOmoz is the safest bet.