By the time you need DOT 5 brake fluid, you're a professional racer. The boiling point of modern DOT4 fluids is fantastically high, and you don't even have to spend a lot of money on it. Valvoline SynPower is a very high performance brake fluid found at any autoparts store or Wal-Mart.
I have used it on the track. :)
Anyway, if you bleed your brakes every 1-2 years using good quality NEW brake fluid you won't have any problems. Because of the water absorption, it's a bad idea to re-use an old container you might have in the garage. Most brake systems have less than 16oz total capacity and you'll use maybe half that at most when bleeding.