W3Perl have two different modes. One is used to init your stats, the other is used to update.
The average speed is 3500 lines/sec on a XP2500+ so it took around 25 minutes to parse a 1 Gb file or more than 6 hours for a 1 Tb file.
A 1 Gb file is around 6 million lines, it's nearly two years logfile size for a 10 000 hits/day website or two months for a 100 000 hits/day.
If you need a really fast software, use one written in C as Analog or Webalizer.

star Initialisation

Running in this mode could be quite long if your logfile are huge, but you'll need to run it only once. So after a successfull installation, you just have to run the 'cron-w3perl.pl -a' command (or use the admin interface) which will compute everything from scratch.
If you make important changes to your configuration file, you maybe need to re-init your stats or any changes you have made will only occur for the next incremental run.

star Incremental

This is the update mode. The scripts are designed to be run once a day.
To avoid unecessary CPU use, incremental stats are computed between the last run and today. By default, the maximum number of days between two incremental run is 7 days but it could be change. Time taken to update all your stats is a few minutes depending on your average logfile increase. Running 'cron-w3perl.pl -e' will update all your stats.
A day took typically 3 seconds to compute for an average 6000 hits/day website and 15-20 seconds for a 40000 hits/day website.

star Initialisation benchmark

To give an idea how long it could be, this is the time taken to complete the stats on my XP2500+, 512 Mb RAM.

Website Intervalle Logfile size Hits / day CPU Speed
W3Perl 1216 days
(40 months)
1.7 Gb (124 Mb compressed) 6 000 41 min 50 3550 lines/sec
INRP 129 days
(3 months)
1.2 Gb (154 Mb compressed) 61 000 39 min 26 3970 lines/sec
(Logfile 1.7 Gb) CPU Speed Relative speed
reverse dns off 41 min 50 3550 lines/sec 100 %
geoip_free module 1 h 02 min 55 2280 lines/sec 65 %
netgeo module 1 h 04 min 15 2280 lines/sec 65 %
reverse dns on 9 h 12 min 20 270 lines/sec 7 %

Level of precision is by default three and reverse dns is off.
Compression rate is around 90% of raw logfiles.

To get speed increase, disable reverse dns (very slow) but you won't be able to get country stats. If you really need country stats, use the Geo::IP perl module (which is a reverse dns file stored locally) or use the fastresolve tool to translate IP to hostname before running W3Perl. Turning off robot detection or referer spammer filtering can increase speed also.

Avoid using the highest level of precision with huge logfiles as it will require a lots of RAM to process.