Long quick links are more versatile. They have a wider gate opening. 

The "high-strength" version quick links are made with a slightly larger nut and wider threads adding better holding power.

Climbing Taiwan's break test videos & results:

10 mm 316 SS Zoutianya:  54.90 kN

8 mm 316 SS Climbing Taiwan  (high-strength) : 69.49 kN, 69.14 kN, and 69.42 kN Video

8 mm 304 SS (high-strength) Ningjing : 68.66 kN Video

7 mm 304 SS Barhar : 52.80 kN, 52.95 kN Video Video

7 mm 304 SS (high-strength) Ningjing : 51.27 kN, 46.50 kN, 50.61 kN Video

6mm 316 SS Climbing Taiwan  (high-strength):  37.91, 38.88, 37.85, 38.13, 38.25, 38.31, 39.32, and 38.12 kN  Video

The quick links have stamped ratings from the manufacturer.