In another thread I started about MP5's and AR/9mm's, colt owners say that they had to replace their bolt's and buffers to get a decent rate of rife and eliminate trigger slap.  They said these modifications brought their colt FA's close to the characteristics of FA fire that an MP5 has.

Since we're measuring up to the MP5 as the standard, what modifications if any do Oly's need to reach that level?

Trigger slap with Oly will be non-issue, as Oly uses a std AR carrier with a bolt head stuck in the front, thus it will have an everday cocking ramp that the hammer follows as carrier goes rearward, just like 223.
Colt 9mm bolts have goofy ramp geometry, that creates a harsh feel and the hammer has a tendancy to tear up pins, to get thrown rearward and hit the disconnector, and transmit into trigger.
Re-profile of Colt style bolt eliminates this problem. Ken at SAWLESALES does this mod, and adds a weight to the bolt to help slowdown the rate of fire.. heavier buffers can used to slow down rate of fire in auto mode, but for semi, buffer is not very important.
Amphibian has posted a pic of his bolt somewhere I think after the mod by Ken (Colt 9mm style).