Such comparisons depend on the selected problem very much. Several years
ago, the speeds of sparce polynomial multiplication by various CASs were
compared:
http://www.cs.berkeley.edu/~fateman/papers/fastmult.pdf
Namely, the polynomial (1+x+y+z)^20 (expanded) was multiplied by itself.
And maxima (compiled with cmucl; sbcl should not differ much) was several
times faster than maple. Reduce was fastest among general-purpose CASs,
Mathematica was slowest. True, the versions of all CASs were rather old;
it would be interesting to repeat this benchmarking with more modern
versions.
Andrey