Your expression has "1/x^3" in its exponent. The expression from the orginal post would be 27**(log(x,3))/x**3, which SymPy correctly simplifies and finds the correct limit for:
>>> simplify(27**(log(x,3))/x**3)
Integer(1)
>>> limit(27**(log(x,3))/x**3,x,oo)
Integer(1)
Other examples of wrong limits with logarithm in exponent in Sage:
lim((((27**(log(n,3))))/n**3),n=infinity) returns 0 (
Wolfram Alpha and Maple return 1).
lim((((27**(log(n,3)+1)))/n**3),n=infinity) returns 0 (
Wolfram Alpha and Maple return 27).
lim(((27**(log(n,3)+1)-1)/26+n-log(n,3)-1)/n**3,n=infinity) returns 0 (
Wolfram Alpha and Maple return 27/26).
Using SageMathVersion6.7, ReleaseDate:2015−05−17.