What CMS should I choose for this project.

[unknowngiver]

hey,
I am an engineering student, but I like developing websites and coding in PhP [still a newbie programmer] but I havent been able to create any websites lately because of the heavy workload i get from my engineering courses. So, I am thinking about combining both of my passions and making a website with engineering tools (calcultors for various functions, e.g calculating work done on systems, or horsepower etc) and writing articles (summarizing what I learned) etc.
I dont want to make a website from scratch, but rather use a CMS so its easy to manage (since it will be a massive website, with thousands of calculators) and effective (in terms of SEO and layout)

I have used Joomla, and Drupal before, and like both of them, however I don't know which CMS will be the best for this project.
My calculators will be pretty much a bunch of funtions in PhP, for example

function area(dim,shape)
{blah blah..calc area
return calculatedarea;
}

I really want to use Ajax in my website and make it more web2.0 design.
Recently I came across MODXCMS and it looks great, and promises an easy Ajax adaptability or what not, but It was a bit challanging to use.

SO, I want to know what CMS will be best for my needs, and why
I will donate NP$ for good answers
Thanks