Problem with 35 DEF is that some pax use this as a path to the toilet.
35D is also very close to the loo, so if the flushing niose bothers you, maybe avoid. 35JK would be the best IMO.
Upstairs is great, I always get wines from Business.... just ask when the CSO first comes to say hello, they give you a real glass that is a code to the other attendants.... you get the 'good' wine for the whole trip. My wife and kids all got biz cheese plates last week, they were all left over.
Having said that, having a chat with the CSO on DXB->SYD, he indicated that QF always leave 10+ seats on the DFW runs (which were his usual runs) as they have a lot of cargo, so lower deck from DFW is a no brainer.... take the second last row aisle seat D or G, and you will likelyu have the whole row = nice sleep.