Selecting Rear Surrounds for 5.1 system

Hello

I would like to get some advice on selection of rear surround speakers for my 5.1 system.  I have repurposed my formal dining and living to an A/V room and it is

23 feet long and 12 feet wide and ceiling is 10 feet high.

I have B&W 702 S3 fronts with HTM72 center & Polk 12" sub with Marantz 7015 amp.  I've placed the chair 14 feet from front wall (12 feet from front speakers).  What type of rears would make sense.  I was thinking about Polk R700s - is that a silly idea.

Thank you