Railguns should have the same rate of fire as an equal sized laser, unless things have changed.
That seems to be the case, but higher-level lasers seem to be generally smaller than higher-level railguns (well, I can't really tell, since I'm only at size two and strength 2 for both, but the comparisons at this level don't seem very favourable for the railgun).
Here's a 10cm VL-laser compared to a 10cm Vel2 railgun:
Damage Output 3 Rate of Fire: 10 seconds Range Modifier: 2
Max Range 60 000 km Laser Size: 3 HS Laser HTK: 1
Power Requirement: 3 Power Recharge per 5 Secs: 2
Cost: 6 Crew: 9
Materials Required: 1.2x Duranium 1.2x Boronide 3.6x Corundium
Damage Per Shot (4): 1 Rate of Fire: 10 seconds Range Modifier: 2
Max Range 20 000 km Railgun Size: 3 HS Railgun HTK: 1
Power Requirement: 3 Power Recharge per 5 Secs: 2
Cost: 6 Crew: 9
Materials Required: 1.2x Duranium 1.2x Boronide 3.6x Neutronium
The railgun has a higher damage potential by 33% for the same size at the same RoF, but only 33% the range. So, superior in close quarters. The question remains how exactly the low tracking speed will affect precision. It does indeed seem predestined for a fighter weapon as suggested, where the ships' maneuverability will improve the tracking, and where a laser would suffer the same disadvantage due to no turret. So far so good.
Here's a comparison of a 12cm VL-laser and a 12cm Vel-2 railgun:
Damage Output 4 Rate of Fire: 10 seconds Range Modifier: 2
Max Range 80 000 km Laser Size: 4 HS Laser HTK: 2
Power Requirement: 4 Power Recharge per 5 Secs: 2
Cost: 8 Crew: 12
Materials Required: 1.6x Duranium 1.6x Boronide 4.8x Corundium
Damage Per Shot (4): 2 Rate of Fire: 15 seconds Range Modifier: 2
Max Range 40 000 km Railgun Size: 5 HS Railgun HTK: 2
Power Requirement: 6 Power Recharge per 5 Secs: 2
Cost: 9 Crew: 15
Materials Required: 1.8x Duranium 1.8x Boronide 5.4x Neutronium
The railguns damage potential is now a whopping 100% higher than the laser's, while the range is only halfed. That looks like a great development for the railgun at first glance. However, this is a bit mitigated b the railgun being 25% larger and having its RoF increased by 50%. That means the effective damage potential per minute is exactly 33% higher. . . In effect, we get a better range comparison for a larger size at same relative damage potential. Still, it's an improvement over the 10cm comparison.
But now starts the tracking problem, since this gets a bit too big to put into a fighter, though it could still go well with an FAC. While (depending on turret technology) the laser will be larger, it does retain the range advantage, but will be much more precise, possibly mitigating the higher damage potential of the railgun. . . I say possibly, because that's really the question now. The comments here that railguns are great PD weapons give the impression that the tracking penalty isn't actually that big of a deal (otherwise they'd never hit any missiles). Just how big of a deal it is would be really interesting to know before spending more research on railgun size.
If it's not that big of a deal, from what I see currently the railguns will retain their advantage of damage potential while mitigating the inferior range more and more up the tech-tree, which could make high-level railguns extremely deadly weapons.
Otherwise, they might make a good weapon for some kind of cap-ship killer type vessel that is more maneuverable than the big boys and can bring the full damage advantage to bear against them while not suffering too much of a range disadvantage. But I'm not sure yet if such a specialised class would justify the research cost of higher-level railguns along with high-level lasers, which would still be needed for the really heavy hitters.
Might be considered a question of fleet paradigm, I guess.
EDIT:
Ah well, through trial comes expierience. . . With a higher recharge rate the 12cm railgun can be brought to the same RoF as the laser. We're talking a full 100% more damage potential then. If this trend increases on higher levels, then railguns should be able to hold their own against lasers. The only problem would be armor penetration, the precision should be made up by the salvo fire. Hmmm. . .