One of the problems in trying to establish which football player was faster is that some of them never ran track, officially, so there are few official records for players like Desean Jackson and Wesley Walker. There are some 40 yard dash recorded times for most football players, so at least we can compare those. A second problem is that track times are recorded on track surfaces of different composition from era to era, and very different from football 40 yard dash races, where the players wear cleats and run on grass. Another problem is that times are accurate to 1/100th of a second now, as opposed to 40-50 years ago when times were only accurate to 1/10th of a second, and wind was not taken into account as much as it is today. Here a some records of former Cal players:
Desean Jackson ran a 4.35 second 40 yard dash in 2008 at the NFL Draft Combine. He is reported to have run a 10.5 second 100 meter dash, but I could find no official source for that.
Jahvid Best was both a track man and a football player. He ran a 4.35 second official 40 yard dash, and a 4.33 second unofficial one. In track, Jahvid Best was a world class 100 meter sprinter, and ran an official 10.36 second time as a high school senior in 2007. He also ran a 10.31 second wind assisted time in 2007, a 10.26 wind-assisted time in 2015, and an official 10.35 second time in his heat in the 2016 Olympics, finishing in 7th place behind Usain Bolt, who ran 10.07 seconds. Best also owns an official time in the 200 meters of 20.65 seconds.
Thanks to Big C for bringing up Wesley Walker. Walker apparently did not run track officially, but ran an official 4.38 second 40 yard dash while with the Jets, and I could find no other times for him.
Thanks to Joe Amos Yaks for bringing up Isaac Curtis. He played at Cal only a couple of years before Wesley Walker and ought to be considered in the discussion. Curtis ran a 4.4 second official 40 yard dash time in 1973, and 12 years later in 1985, he ran an official time of 4.5 seconds. As a member of the Cal track team, Curtis recorded an official time for 100 yards of 9.3 seconds, and finished 2nd in the 1972 NCAA 100 meters to Cal's own Eddie Hart, perhaps the best sprinter in the world at the time, with both men timed in 9.4 seconds. Curtis also ran an official time of 20.7 seconds in the 200 meters in 1970.
Getting back to the original question of who was faster, Jackson or Best, it is hard to answer because there is little measurable data on Jackson. Based on their 40 yard times, they are evenly matched. Curtis definitely should be in the conversation as his times were only a shade behind Eddie Hart on the track, and if there were more data on Wesley Walker, he would likely be in the conversation as well.
Finally, a word on that NCAA Championship in 1972. Cal had not won an NCAA track and field title in 50 years. In 1972, Hart and Curtis finished 1-2 in the 100 yard dash, Curtis finished 4th in the 220 yard dash, and they both were on the 440 yard relay team that won a Gold Medal. Together with a few other Cal athletes who placed in different events, Cal scored enough points and won the NCAA Championship. Later that year, during football season, it was determined that Curtis did not take the SAT exam under appropriate circumstances, probably the football coaching staff's fault, and the NCAA title and all the records were vacated and taken away from Cal and the athletes. A black day for Cal track and field fans, and Cal fans in general.
SFCityBear