Standard striker spring is 5.5, not 5.0. Unless you have (or reload) ammo with extremely hard primers, there's no need to increase your trigger pull by installing a still heavier striker spring. You don't identify the gun, but possible exceptions might be the .45 and 10mm because of a heavier striker; no experience with those but I understand some use the extra power 6# striker spring with those models.
Combining the 6# trigger spring with the very weak 4# striker spring can result in the trigger failing to come all the way forward. However, you need not reduce the striker spring all the way from 5.5# to 4.0# to get a reduced trigger pull. There are 4.5# and 5.0# springs, and either of these springs should be sufficient to ignite the primers of most ammo (especially SD ammo) AND reset the trigger all the way forward. If you want additional margin against light strikes, a lightweight striker like the Jager can provide it.
Last edited by bentbiker; 02-09-2013 at 13:25..