Earlier quoted context omitted.
Suppose that you cost $50,000 a year. If a new Sublime Text would only make you 2% more productive, even an upgrade for $100 per year would be peanuts. Start talking to your boss! If you use Sublime Text privately, I can see your point.
It's that kind of rationalization to spend more money that makes other people rich, and I read variations of your justification on HN all the time. A 2% increase isn't very good IMO. I'd rather look for other efficiencies that won't cost me more money.
If you are saying there are efficiencies elsewhere for which that formula yields a higher number then you should do those as well.