BSNES has a somewhat different purpose to most emulators; it focuses on accuracy over performance. To that end, it does not include any game specific hacks, or idle-loop skipping optimizations commonly found in other emulators. To add to the fun, it uses a cycle accurate hardware emulation. The net result of all this is the highest system requirements of any software I've released to date; those without a G5 class machine need not apply. If you meet the requirements, however, this is the most accurate SNES emulation available on the Macintosh platform.
BSNES requires a minimum of a PowerMac G5 to run. The current release is unlikely to run at full frame rate on anything less than 2.3GHz. Those who do not meet the minimum requirements should be able to run the program anyway by command-clicking the OK button in the system requirements dialog box, but this facility is completely unsupported.