I have RF-35 front speakers and RC-35 center.  I am looking to get surrounds, and wondered if the RS-7 would work ok in conjunction with them.  I am also looking at the RS-52 if I can't find either the RS-35 or RS-7. Would any of these choices be bad for blending of the sound? 

I have 5.1 set up of 35's. I also had to hunt down the RS35, worth it in the end.

I can't speak for any other Klipsch surround but the RS35 does blend in very nicely.

Not to worry you are in very good hands on this site.

RS-52s will match better than RS-7s.  The 7s have higher sensitivity than needed, are larger than necessary and more costly.