I5-520 versus i7-720 for single-threaded application

Hello,
I'd like to know which processor, the i7-720 or the i5-520, will run what I assume is a single-threaded program faster. The program creates a crossword puzzle, beginning in one corner of the crossword and working its way across, finding all the words, or word combinations, that fit together. It's time-consuming but not really very complicated, and in fact my desktop with an ancient Pentium usually runs the program just fine (although it does take a while), but I was wondering which chip would run it faster (assuming the same RAM and drive speed in the competing setups.) I do not run any other programs at the same time.