805k Vs Q9BK

Been looking for a 75"-80" TV, specifically in costco for the warranty. was originally going to get the 845k at £950 but it went out of stock before I bought. I can see the 805k for £900 or the Q9 for £1250. I can't seem to find much difference in the specs between the w to justify the extra 40% increase. Any suggestions, or info please?