Here is a small benchmark comparison of 3 archivers -- paq8o8, 7zip 4.47 beta, and LZPM by ilia_muraviev ....

The file is calgary.tar - available from URL
- A standard benchmark file.... starting size - 3,152,896 bytes
The system is an athlon X2 4200, running Vista 32 bit, with 2 Gb memory.

Paq8o8 - level 8 - (currently worlds highest general compression)
final file size - 594700
time used - 383.60 seconds
memory used - 1.57 GB

LZPM --- (-9 option - highest)
Time - 25 seconds,
final file Size - 865,833 bytes
memory used - unknown

7 zip - 4.42 - ultra - 64MB dictionary, 273 word size-
memory - 709 MB
time- < 2 seconds
Finnal size - 819,982 bytes

Not a bad job for LZPM, but 7 zip is still way better.