I used 275/35/18s on the 10" 47mm rears on my old 01S. This size really filled out the wheel nicely. (BTW, the tires are for sale in the classifieds - shameless plug.) Your 265 will work but it may be a stretch for that wheel. There won't be much tire sidewall protection of the wheel lip. I went with 275/35 because there were more choices available in that size that were reasonably priced. There's quite a price jump when you go to 285/30, mostly because there are fewer manufacturers.
Also, according to the handy-dandy wheel offset calculator, going from a 9.5" 43mm wheel to a 10" 47mm wheel will move it inward by 10mm (approx 1/4"). That's a healthy move. Might want to see if there are going to be clearance issues. Some spacers may be required. On a 986 it's an 8mm move (9", 52 to 10", 47) and there are issues with the e-brake cable. Don't know what might be lurking on a 987.
Good luck and enjoy.