I thought that may be a possibility too, hence thinking a second panel, and possibly a better one down the track, I've been having heating/cooling issues, which I'm struggling with, with just one 600 hps, is an old house, the interior walls are clad with asbestos sheeting, with a 14ft ceiling, and once the room heat passes 23° Celsius I can't control the heat in the tent.... So with a ventilation upgrade, I'll need hoping, I can run the 2x600 hps at 400w or less and have leds to supplement, then my grow area temperature will be under control but still getting as much light on the ladies!
at some point your gonna want to just pull the trigger and go all led. the power savings are great, but it's the increased control over environment that really makes it worthwhile. your heat issue would be a lot easier to control or non-existent. in my veg space i add heat in, if i ran hid i would be trying to pull loads out.
edit : not to mention there's a safety factor with most new led rigs that just doesn't come with hps. led is a lot easier on the wiring.