Dimensions and Weight
Both the black and silver version of the Hero4 are the same dimensions of both the Hero3 cameras (41mm x 59mm x 21/30mm). This means all cases for the Hero4 and Hero3 are interchangeable. The weight, however, differs the two. The black version of the Hero4 is 88g without housing, and 152g with housing. The silver version of the Hero4 is 83g without housing, and 147g with housing. This is a significant difference from the Hero3’s 74g without housing, and 136g with housing (both versions). The Hero4 silver edition is the only GoPro that has a permanent LCD screen, which is why it adds more bulk.
Field of View(FOV), Lens Aperture, and Sensor Size
Despite many differences, the Hero4 and Hero3 have some similarities. The FOV(ultra wide, medium, and narrow), less aperture(F2.8), and sensor size(1/2.3”) are the same for both models.
Video and Audio
Out of the four models and editions of the Hero3 and Hero4, three out of four have 4K video recording. The Hero4 black edition at 4K has 30, 25, and 24 FPS (frames per second), and at 2.7K has 50, 48, 30, 25, and 24 FPS. The Hero4 silver edition and the Hero3 black edition at 4K has 15 and 12.5 FPS, and and at 2.7K has 30, 25, and 24 FPS. The Hero3 silver edition does not support 4K.
With video quality it’s no surprise that the new Hero4 kills its younger versions. The Hero4 black edition at 1080p offers 120, 90, 60, 50, and 48 FPS, and at 720p offers 120, 60, and 50 FPS. The Hero4 silver edition at 1080p offers 60, 50, and 48 FPS, and at 720p offers 120, 60, and 50 FPS. The Hero3 black edition at 1080p offers 60, 50, and 48 FPS, and at 720p offers 120, 100, 60, and 50 FPS. The Hero3 silver edition at 1080p offers 60 and 50 FPS, and at 720p offers 120, 100, 60, and 50 FPS.
With the current slow motion craze, the Hero4 really sets itself apart from the competition. The Hero4 black edition at 120 FPS handles 1080p, 960p, and 720p, and at 240fps supports WVGA (Wide Video Graphics Array). The Hero4 silver edition and the Hero3 black edition at 120 FPS handles just 720p, and at 240 FPS also supports WVGA. The Hero3 silver edition at 120 FPS handles 720p and supports WVGA.
As far as bitrate goes, the Hero4 black edition obliterates the others. The Hero4 black edition tackles 60mb/s. The Hero4 silver edition and the Hero3 black edition manages 45mb/s. While the Hero3 silver edition tries to keep up at 25mb/s.
All four editions boast a mono microphone with an optional 3.5mm input. However, the Hero4 black edition goes a step farther and offers a analog-to-digital converter.
Still Photos
Both Hero4 editions and the Hero3 black edition support 12MP pictures and 30 FPS in burst rate mode. While the Hero3 silver edition carries 10MP pictures, and puts up 10 FPS in burst rate mode.
Superview and Protune
Superview is a GoPro speciality mode that uses a 4:3 aspect ratio, the full height of its sensor, and stretching the original aspect ratio to a widescreen 16:9 aspect ratio.
The Hero4 black edition isn’t even a fair fight compared to its competition — it’s available in 4K, 2.7K, 1080p, and 720p. The Hero4 silver edition and the Hero3 black edition only allows Superview in 1080p and 720p. 
The Hero3 silver edition does not support Superview.
Protune allows GoPros to capture higher quality videos with less compression. Both Hero4 editions support Protune in both videos and stills. The Hero3 black edition supports Protune in videos. Lastly, the Hero3 silver edition does not support Protune.
Wireless, Storage, and Battery
Both Hero4 editions support Wi-Fi and Bluetooth connectivity, while both Hero3 editions support only Wi-Fi connectivity. All of them are compatible with the app and remote.
Both Hero4 editions and both Hero3 editions allow for microSD storage.
Battery life is where the older editions have the advantage. Both Hero4 editions offer a 1160mAh battery, while both Hero3 editions boast 1180mAh batteries.
Price
Lastly we have prices.
