The 5.0 cobra's were high 14's in the 1/4 usualy.. the weight and power in them is just slightly better then the stock 5.0 of those years.. which were in the 15's quite often. The DOHC 4.6 was a huge bump in stock output.

No idea what the Cobra R's run.... only 250 of them made that year I believe.. very very rare car.

EDIT*
I'll just throw all these out there for ya. I was wrong, mid 14's. lol.

1990 Ford Mustang LX 5.0 6.4 14.9
1991 Ford Mustang GT 7.3 15.6
1992 Ford Mustang LX 5.0 6.2 14.8
1993 Ford Mustang Cobra 5.9 14.5
1993 Ford Mustang GT (auto) 8.0 16.1
1994 Ford Mustang Cobra 5.4 14.5
1994 Ford Mustang GT 6.1 14.9 (C&D Dec '93)
1995 Ford Mustang 3.8 9.9 17.3
1995 Ford Mustang Cobra R 5.2 13.8
1996 Ford Mustang Cobra 5.4 14.0
1998 Ford Mustang Cobra SVT 5.4 14.0