When building "unrar" from Source do not forget to set "-DALLOW_NOT_ALIGNED_INT". This provides a huge performance benefit for encrypted files.
I use:
make -f makefile.unix CXX=g++ CXXFLAGS="-O2 -march=pentium3" DEFINES="-D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -DLITTLE_ENDIAN -DALLOW_NOT_ALIGNED_INT" STRIP=/bin/true DESTDIR=/usr/local