You can't generalise - it's not the same in every case.

For example, suppose links, content and optimisation each contributed to the ranking score in equal proportions - 33% each. That doesn't necessarily mean that, if a page has no inbound links, content and optimisation will still contribute equally, ie 50:50. Under these circumstances, the algorithm may behave differently - it could be 60:40 one way or the other. Or more likely, the algorithm gives added weight to one particular element, such as the page title.

So you really can't give percentages, but in general terms, optimisation beats content on Google if it's done thoroughly and without spamming. Enough inbound links with keywords in the anchor text will trounce both, if they are from relevant well-ranking sites.

W3C validation is for disability access (and coding purists). Neither search engines nor browsers give a toss about it. If the page displays OK in IE and Firefox, it will be OK with Google.

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Bruce Townsend
Actinic ecommerce software, ecommerce website design