Can i use pc3-10600 with pc3-8500 on my imac end 2009??

actually i have a Imac end 2009 with 4Gb DDR3 PC3-8500 1067MHz

I need more ram but i found 4Gb DDR3 PC3-10600 1333MHz... My question is if i put the 4Gb PC3-10600 with my 4Gb PC3-8500 my imac will work properly?

I suppose the memory 1333MHz will probably work at 1067MHz.. Or i need to change all the Ram for a new one?

Thanks!!

(Sorry, i'm french, my english is not really good! 😉 )