I use xlcompare for comparing Excel. It creates very good diff reports of Excel features (including formatting, formulas and Macros). I often use it for simple CSV compares. Be warned, it does crash occasionally
I have used a Macbook Air 13" (i7 2GHz, 512GB SSD, 8GB RAM) for over a year exclusively for software development. The machine has been great, except I am frequently swapping windows back and forth, because of the screen resolution (1440x900).
I develop using numerous tools including Emacs, Xcode, IntelliJ, WebStorm and Visual Studio (running inside VMWare Windows 8 Pro). I have never noticed any lag whilst coding
Would I buy the same size machine again? Yes. The trade off is weight against screen size, although I think a higher resolution screen might put a strain on my eyes considering how long I use the laptop.
For me desktop was never an option, because I code on the train often. I also do not use either an external monitor nor a keyboard.
What type of freelancer, because the rates can differ by a large margin for different roles? Web designer, technical writer, developer, architect, SAP, Oracle DBA, etc.
I also find that generally, in Europe, today's rates are daily. With the assumption that the working hours are at a least the same as those of an employee; but, often expected to be one or two hours more (banks, I'm looking at you).
I am Swiss-based and for senior software developer roles my freelance daily rate is equivalent to USD1000 (one thousand) per day. The contract duration has no relation to my rate.
Although, I agree with zacharyvoase that I do not see the point of your question.
https://www.xlcompare.com