be careful, claiming to do well with an archer often produces hate on these forums
(but i believe you, my ingame archerfriends aren't as pessimistic as the forums)
Joking aside though:
RR5 unlocks 16,5DPS on weapons, before you only utilize 16,2DPS.
Additionally an RR3 Assassin will (probably) have purge2 vanish1 and longwind/tireless = 2L7. So not much left for damage RAs
At RR5 you have 20more points than at RR3. 20points buy MoP7 which gives you a 29% bonuschance to crit. (not saying that is the best investment, just an example to show what 2RRs difference make)