If you already have some CREE's and some drivers...here is what I would do.  I don't think the 8 XM-L's will be enough.  I would buy a small mix of Modularled White and Royals and add them along with a small driver to the mix you listed above with the 8 XM-L's (assuming you have these already).  That heatsink can handle a lot of LED's. This should still be your cheapest solution while getting you LED's that you know you can count on. 
		
	
		
		
		
		
			
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				Mark...
  
290g Peninsula Display, 425g total volume.  Setup Jan 2013.
			  
		
		
		
		
	
		
		
	
	
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