The p1000 allows you to move the heatsink outside of your small tent, a massive benefit over the LEDs with a powersupply hardmounted to the board of LEDs, Them being cheaper probably also means less efficient, resulting in more heat being put out.
with the p600 all this heat ends up in your tent, a benefit in the cold winter, but in the hotter months you will be fighting both the heat from mother nature and the heat from your Viperspectra, with the more expensive model you can just move the heat producing parts of the light outside of your tent.