Are highly rational individuals more sucessful?

In my humble opinion, no. Here is why, I think a strong emotional quotient can matter more.
Successful people knows that the core of any achievement will depend on personal relationships.
The most successful people are frequently unreasonable people who refuse to give up, even when evidence and odds are very much against them. In conclusion, human skills are more important than cold rational logic.

As an IT Architect how do you measure success (II)?

In respect to what KPI your organization follows or not, The simplest way for IT architect (matters any Architect) to measure his/her success is:

1) Develop your growth plan for short term and long term, what and where you want to be.
2) Knowledge Acquisition in changing business demands.
3) Build a design or solutions were all business elements (People process and Technology) are met and bridge all the gaps.
4) Achieve excellency in your work to gain buy-in for all your plans and designs.
5) Request Testimonial/Recommendations for your work (efforts are useless if you're not appreciated).

If you are done with above, you are on TOP success list, rest will follow :)

As an IT Architect how do you measure success (I)?

In my opinion the success is measured by:

Was the solution implemented?
Did it provide the expected results?
and finally, Is the solution flexible enough to withstand change?

I mention the last one because IT is built on top of change. Any IT Architect (of any vertical) must incorporate the change aspect on its solutions. Please do not reduce the support for change just to the upgrades and additions to the solution. The end-of-life, disposal and deployment of new solutions also counts as change.