Some stats to chew on:
- 2003 and 2005 were the two years that both Foster and Davis were healthy (although both missed a few games)...most seem comfortable comparing the 2008 situation to these two years.
RUSHING
- In 2003, Foster%s rookie year, he had 113 carries.  Davis had 318.  That%s a total of 431 carries.
- In 2005, Foster had 205 carries.  Davis had 180.  That%s a total of 385 carries.
- The average amount of carries for these two years is 408.
- The blend of carries is in favor of Davis at roughly 2/3.
RECEIVING
- In 2003, Foster had 26 receptions.  Davis had 14.  That%s a total of 40 receptions.
- In 2005, Foster had 34 receptions.  Davis had 5.  That%s a total of 39 receptions
- The average number of receptions for these two year is 39.5 receptions.
- The blend of receptions is in favor of Foster at roughly 3/4.
So, the obvious questions:
- Did Fox favor Davis earlier because he likes the bruiser, or because he was the veteran?
- Why did Foster%s carries increase over the two years?  Was it because the younger player was improving, or because the vet was breaking down?
- No one knows outside of the Panther organization, if not Fox%s own head.
My $0.02: I don%t consider the Foster/Davis combo to have the same combination of skillset as Williams/Stewart.  DW/JS are both better receivers, for instance, and I%ll go out on a limb to say I think that they%re collectively more talented.  That said, I am comfortable assuming an average of 408 carries and 39.5 receptions between the two of them.  My personal opinion is that this will wind up as a very balanced RBBC (since I believe that their skills are more balanced), with half the production coming from each.
So, it%s safe to predict...
- 204 carries each.  At 4.0 ypc, that%s 816 yards on the ground.
- 20 receptions each.  At 9.5 ypc, that%s 190 yards on the ground.
- That totals 1006 yfs for each.
Assuming good health for both, and modest TD performance, that lands BOTH of these backs square in the middle of RB2 territory.  I would guess that the TD performance will be the measurable to elevate one player%s FF stats over the other.  We know that it%s dangerous to predict this, but for the sake of conversation, Davis has 20 to Foster%s 5 (80/20).
So, who winds up better?  Predict who scores more TDs, predict who gets hurt, or flip a coin...I%d say your odds of all three are about the same.