I'm writing this up. I ran Einstein's Riddle 100 times under SWI Prolog and Chez Scheme/Shen Prolog kernel S 34.6. I was pleasantly surprised to find the two times were very close.
% 7,208,201 inferences, 0.219 CPU in 0.578 seconds (38% CPU, 32951776 Lips)
(6-) (time (do (prolog? (riddle_n 100)) (inferences)))
run time: 0.265625 secs
To run this problem I had to set (prolog-memory 1e5).
Its interesting that LIPS are counted differently in these two Prologs.