+1 on hire out and test or get a vendor demo. Not knowing the budget, replacing 4 x 2000w FOH/Key Lights with LED could be an expensive endeavor. There are some great LED products from Chauvet Professional (Ovation, Rogue, Maverick Series), ETC (Source 4 LED, Colorsource, Selador) and Elation (Satura, Fuze, Arena) and many other vendors with similar offerings. Some can be run on existing dimmer circuits and some cannot. Other considerations would be the addition of a lighting console to control more complex LED fixtures, possible modifications to electric circuits, and running of DMX control signal cabling. Apologies if you are already aware, but there is another blog called Controlbooth that has a lot of resources and information.