The 500 has a display of 1.17" W X 1.44" H
The 705 has a display of 1.37" W X 1.71" H
The resolution on the 705 is a bit finer than the 500.
The 705 also costs more, so if you don't need the added features, might as well save the money. I like my 705 for the most part, the color display, mapping.
You can compare the 2 here. https://buy.garmin.com/shop/compare....eProduct=10885
I don't think Garmin is or ever will be on top of the game as far as fitness goes, but I like what they have combined gps and fitness. More than anything, it records the data and I can look at it later on my pc. The gps is just a bonus.