Basically my opinion from research is that there is VERY little disparity between black and white speed position players over 40 yards when you discount the guys like Mike Alsott and Peyton Hillis that were made to beef up to block and were no longer ideal weight for a tailback. Or how about Steven Korte? A "FB" who beefed up; still with 4.38 hand-timed speed; didn't run at the Combine and wasn't even considered an NFL prospect b/c of lack of chance in college, despite running for 11 YPC one year in Louisiana in H.S.
Or how about the beefing up of RB Tim Shaw; could have been a slightly faster version of Brian Leonard maybe w/ better vision too, a "Steven Jackson type"? Or how about all the white speedsters who don't have the frame/size to beef up to play safety or are natural RBs instead of wideouts and have to go to the lower college levels due to the Caucasian position ban? (Woodhead, Beaver, Zwinggi, Mueller etc.)
I haven't taken a large enough sample to get a PERFECT picture of black vs. white athletic advantage; but from comparing a couple years of prospect's Combine and Pro-day times of "non-position switch/beefed up" players, I took the top 10 NFLdraftscout natural white speed position guys at Safety, RB and WR and the difference was around .05 seconds slower over 40 yards if I recall for the two years I compared. The difference in distance between a 4.6 and 4.4 40 yard is 1.8 yards. So .05 seconds difference would be about 0.45 yards. or about 1.5 feet; which is basically within arm reach for a tackle.
The black prospects do tend to separate better post-20 yards down-field though; where the whites separate amazingly in the first 10 yards.
Like I said the ELITE white speed prospects make up for a slight disadvantage on average in top-end speed b/c they seem to do a little better than the blacks in 10 yard splits and 3-cone and short shuttle drills. The last two mentioned tests are good indicators of acceleration and agility in the x-y plane.
I had gotten the slasher/ jump cut styles confused in another post:
To reiterate, maybe this is why a higher PERCENTAGE of top white RBs are Cutback/North-south slashers, plus the TOP white prospects seem to break tackles better and (as mentioned) have better burst on average.
The elite black RBs "TREND WISE" seem "to be more likely" to be darting/ jump cutting style scat backs. They don't start and stop momentum as well, but can dart in another direction on the move while losing slightly less speed. But there are lots of exceptions to this trend of course.
Chris Wells, Andre Brown, Shoon Greene, Cedric Scott, Steven Jackson, Marion Barber, Deuce McCallaster, Ricky Williams, Emmitt Smith, DeShaun Foster (Haven't seen much footage, but Walter Payton probably too) Brandon Jacobs, Terrell Davis, maybe even Rashard Mendenhall or Johnathan Stewart form last year are all typical slashing north-south backs. Even ESPN top H.S recruit Trent Richardson and ESPN 150 prospects Cierre Wood and Michael Ford somewhat seem to be north-south slashing guys.
But of course Tom Luginbill has nothing but praise for these Non Melanin challenged backs.
McGuffie, Rex Burkhead, Wegher, Ben Bowen and somewhat Trumpy seem to be a mix of jump cutter and slashing style. John Howell, Cory McCaffrey of last year (and Danny Woodhead too from what I've seen) are more typical small scat-backs.
Personally I like the guys who can make that intial cut to the hole and explode up field breaking though any arm tackle and use angles to get the most out of their yards. These guys are more consistent moving the chains. If you also have great speed this style is certainly more effective IMO; because after your explosion to the hole you can use your vision and speed to take it the distance. If you make adjust your cutting style to both types like McGuffie, Wegher, Burkhead and somewhat Ben Bowen it makes you an INCREDIBLE PROSPECT because each style can be more effective in certain situations.