There is a wide range of opinion on this subject. I got out my copy of the Lyman Cast Bullet Handbook (circa 1973), turned to page 239 and found the following:
"Plain Base Design: Bullets of this design are usually restricted to approximately 1600 F.P.S."
"Gas Check Design: The gas check fits snugly to the bullet base and allows for a higher velocity of approximately 2200 F.P.S. to be reached."
Take it for what it is worth. I am sure there are a lot of variables like condition of the bore, alloy used, lube used, temperature, etc. that are hard to quantify that may or may not cause leading.