Just did some testing of repeater fire rates with various feats and BAB on live, since it seems no one has posted any yet.
Fire rates listed is the % of time taken to fire 100 bolts holding down attack (i.e. no clicking to improve rates of fire) e.g. if I say a 78% fire rate it means it took 78% of the time to fire 100 bolts compared with the base time.
No significant difference between light and heavy repeaters at any level - nearly all variability was within margin of error. There were a couple of outliers, but 1 was in favour of heavy, the others in favour of light. I can't call it.
None of Haste, Action Boost Haste or Ranged Alactiry seems to affect rate of fire (I'm guessing at least RA should - I've bug reported it). Armor of Speed seems to give a very slight improvement to 93% - well off the "15% faster attack speed" listed. It could be within testing error as well.
UpdateFurther testing by other people suggests that haste effects do give improvements, but due to the multiplicative nature of the effects, once you start getting too many e.g. RR + RS + haste the improvement starts becoming hard to tell at times.
Rapid Reload improves fire rate to approx 75%.
Rapid Shot improves fire rate to approx 78%.
Rapid Reload and Rapid Shot combined improve fire rate to about 60% over having neither.
Rapid Reload and Rapid Shot improves fire rate to about 83% over either Rapid Reload or Rapid Shot alone (i.e. improvement is not as good as having either over none, but still a significant improvement).
BAB +14 compared to BAB +1 with Rapid Reload only gave a fire rate of 88%. BAB +13 compared to BAB +0 with both RR and RS gave an improved fire rate of 90%. So let's say BAB difference of 13 gives approx a 90% fire rate.
So, comparing a level 1 Rogue with with no feats with a level 20 Rogue:
BAB only: ~90%
BAB + Rapid Reload: ~68%
BAB + Rapid Shot: ~70%
BAB + Rapid Reload + Rapid Shot: ~54%
Level 1 Artificer with no feats (already has RR) compared with a level 20 Artificer:
BAB only: ~90%
BAB + Rapid Shot: ~70%
Based on this, I would recommend any Artificer using a repeater to take Rapid Shot and use a heavy repeater unless the effects on available light repeaters are better. Other repeater users (e.g. Mechanic) should take both Rapid Reload and Rapid Shot.
BTW Artificers should also take Quick Draw to reduce the activation times of Fusillade and Action Boosts (and swapping weapons of course).
UPDATE
I don't have every possible combination, but here's an update with raw numbers - number of seconds required to fire 100 bolts (smaller is better):
Heavy vs Light Repeater
Code:
Heavy/Light BAB Rapid Reload Rapid Shot Time (seconds)
------------------------------------------------------------------------
Light +0 Y 75
Heavy +0 Y 74
------------------------------------------------------------------------
Light +4 Y 76
Heavy +4 Y 72
------------------------------------------------------------------------
Light +14 Y 68
Heavy +14 Y 69
------------------------------------------------------------------------
Light +15 Y Y 56
Heavy +15 Y Y 57
------------------------------------------------------------------------
Rapid Reload/Rapid Shot
Code:
Heavy/Light BAB Rapid Reload Rapid Shot Time (seconds)
------------------------------------------------------------------------
Heavy +1 100
Heavy +0 Y 74
Heavy +1 Y 78
Heavy +0 Y Y 62
------------------------------------------------------------------------
BAB
Code:
Heavy/Light BAB Rapid Reload Rapid Shot Time (seconds)
------------------------------------------------------------------------
Heavy +1 Y 78
Heavy +14 Y 69
------------------------------------------------------------------------
Heavy +0 Y 74
Heavy +4 Y 72
------------------------------------------------------------------------
Heavy +0 Y Y 62
Heavy +13 Y Y 57
Heavy +15 Y Y 57
Heavy +19 Y Y 55
------------------------------------------------------------------------
Haste/Action Boost Haste (20%)/Ranged Alacrity 10%/Armor of Speed - all with RR and RS
Code:
Heavy/Light BAB Haste 20% Boost 10% Alacrity AoS Time (seconds)
------------------------------------------------------------------------------
Light +10 56
Light +10 Y 56
------------------------------------------------------------------------
Heavy +11 60
Heavy +11 Y 58
------------------------------------------------------------------------
Heavy +13 57
Heavy +13 Y 58
------------------------------------------------------------------------
Heavy +6 62
Heavy +6 Y 58
------------------------------------------------------------------------