For my position, I work regularly in Linux, OSX, Windows, iOS, and Android. Productivity and not just dicking around.
I just bought an Asus T100 for $350
https://www.asus.com/Notebooks_Ultra...mer_Book_T100/
God damn one of the best laptops I ever owned because it gives you the fully realized Windows 8.1 experience. You begin to completely understand the purpose of Windows 8.1 on a device like the Asus. For $350, it's an iPAD AND Macbook Air killer. It only has 2GB of ram and it's lightning fast.
I agree with iwantchixx, you have to try it. I thought I would hate Metro, but I don't. There's some annoying UX choices, but the overall intent and execution is good. For your purpose of spreadsheets, IM'ing, web, etc, Windows 8.1 is perfectly fine.
As others have said, Windows 8, with the 7 "skinning" is great if you don't have a touchscreen monitor on your desktop.
Again, I would like to recommend the Asus T100. If you want to be productive, yet have something to relax in bed to read or browse, the Asus beats the macbook air and the ipad hands down (and I own 3 ipads and a Nexus 7 FHD).