Just my 2cents...i ordered STOCK plugs for my car from napa,what they sent was PFR5 something plugs,the same ones i pulled out of my car.i have never seen a BKR number as stock,only platinum 5 and 6 heat ranges.its not smart to use a non-platinum plug in an sr,but u can if you wnna be cheap.
i recently changed from the number 5 platinum to the six,now it doesnt idle good,but stills drives fine...
also,u shuoldnt gap platinum plugs,they are pre-gapped for your vehicle and gapping them usually damages the electrode,not always,but most of the time.ive done it,im a mechanic.
again,just my 2 cents,it comes down to personal preference in the end