I've been researching heart rate monitors and trying to figure out which one to get. I found this comparison chart on garmin's website. The 910 has the virtual racer, training effect, barometric altimeter and swim metrics over the 310. the highlighted rows indicate the differences in options.

I'm open to anyone's suggestions on gps heart rate monitors good for use in triathlon training. I'm going into my second year of training and am looking to become more effecient with all 3 workouts.

https://buy.garmin.com/shop/compare.do?cID=142&compareProduct=90671&compareProduct=27335