The thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) are extracted from its high-bias (I-V) electrical characteristics over the 300-800 K temperature range, achieved by Joule self-heating. The thermal conductance is approximately 2.4 nW/K, and the thermal conductivity is nearly 3500 Wm(-1)K(-1) at room temperature for a SWNT of length 2.6 mum and diameter 1.7 nm. A subtle decrease in thermal conductivity steeper than 1/T is observed at the upper end of the temperature range, which is attributed to second-order three-phonon scattering between two acoustic modes and one optical mode. We discuss sources of uncertainty and propose a simple analytical model for the SWNT thermal conductivity including length and temperature dependence.