Tested 4 files (2,4 GHz dual core, 4 GB RAM).
Note that the Precomp values are including recursion and additional streams like bZip2, so they are only rough guides - and I intentionally picked the ZIP+ISO to show files where Precomp only recompresses partial streams.
file size ref (level 6) comp/decomp time precomp -cn -intense -t-j
advcomp1.pdf 108,823 126,612 -> 76,077 1.8 s / 1.2 s 125,656
FlashMX.pdf 4,526,946 27,509,105 -> 3,106,490 1 min 48 s / 24 s 26,953,437
setup_paserver.zip 15,235,901 37,706,637 -> 11,751,787 1 min 33 s / 39 s 17,189,024
corellinux.iso 473,825,280 1,017,498,081 -> 429,283,695 1 h 55 min / 49 min 505,421,167
Both FlashMX.pdf and corellinux.iso aren't restored correctly. For FlashMX.pdf, it seems to be a minor bug, there's one removed byte at position 0x29242 and the remaining content seems to be identical (though shifted one byte). For corellinux.iso, there are 5 streams and especially the biggest one takes much time:
It seems that this one is somehow (partially) lost after restoration, file size is only 26,460,730 bytes, there's one byte mismatch at position 0x154E341 (0x46 instead of 0x00) and everything else is identical, though the file is much too small. 473,825,280 - 447,381,529 = 26,443,751, so it seems restoration of the stream was started, but something went wrong after ~17 KB.
00000004.hif 91.069.876 bytes
00000004.raw 447.381.529 bytes
00000004.unp 894.828.544 bytes
Another interesting detail on corellinux.iso: RAR of the original file is only 344 MB and although Precomp can only recompress a part of it successfully, Precomp+SREP+7-Zip gives 318 MB, so the reflate result (429 MB) doesn't really match the successful decompression of almost 1 GB data with relatively small overhead of 90 MB. Perhaps the compression needs some tuning for big files, long matches and such (EDIT: No it doesn't, see below). I have skipped ref0 to save time, will try this on corellinux.iso and edit (EDIT: Just fine, 325,613,370 bytes).
EDIT: Seems the big stream of 447 MB is a misdetection - there is no big deflate stream inside the ISO, but several hundred GZip streams - it seems detecting the stream end somehow fails - this also explains the bad compression ratio as the 1 GB decompressed data also contains artificially "decompressed" data outside of the deflate stream.
Precomp -c- -d0 -t-b output for corellinux.iso:
Ah, the rawdet output for corellinux.iso also shows some strange error, the last stream has no end (but beg=0193C23A=26,460,730, which was the size of the incorrectly restored file):
New size: 492927220 instead of 473825280
Recompressed streams: 1508/1883
ZIP streams: 83/86
GZip streams: 1396/1768
GIF streams: 29/29
You can speed up Precomp for THIS FILE with these parameters:
beg=001F469E last=0 type=2 size=4096 unplen=27590
end=002EDFD2 bufbeg=00000003 bufend=00000000
beg=002EE00A last=0 type=2 size=4096 unplen=144788
end=003348A3 bufbeg=00000000 bufend=00000000
beg=0154C560 last=1 type=1 size=7299 unplen=28307
end=0154E342 bufbeg=00000007 bufend=00000000
beg=015FF016 last=1 type=2 size=1792 unplen=13139
end=015FFA3F bufbeg=00000002 bufend=00000000
beg=0193C23A last=0 type=2 size=65536 unplen=65536