I did a rough comparison between raze planet and siege platforms once (discounting the attack power of the capital ships themselves).  While it wasn't a meticulous test, my findings were that a siege platform did approximately as much damage as one use of raze planet of equal level over the course of its life.  Seeing as the cooldown of siege platforms and raze planet are equal, the long-term DPS of these abilities is the same.  Of course, raze planet is instant damage, costs less antimatter, and cannot be interrupted by killing a fragile platform, so it's better in every other way.

As far as sheer damage, siege frigates are the better deal than capital ships.  The catch is fragility; siege frigates drop like flies if attacked by fighters or scouts, and are pretty vulnerable to just about everything.  As I've said repeatedly, it's well worth your time to invest in a tough siege capital ship.  Less damage, for sure, but it won't even get scratched by these silly antics.  Anything short of LRF spam or bomber clouds isn't going to stop it from completing its job.  A siege frigate won't even have time to run away if it comes under attack, it's just so pathetically fragile.

uh...lvl 6 egg???

dont think anything can touch this in planet sieging

Yeah, I know.  Siege frigates suck.  But, often you have no choice.  Still, I am looking for some direct comparison, as to which is the quickest?  Maybe late game, when you've begun to overrun the oppenent, there's little opposition left, and you need to take out planets quickly.

Advent definitely got shorted when it comes to killing planets.  They don't have much.  It takes too long to level up a Revelation to level 6.  And even then, it is still slow against weak planets, so you are forced to go with frigates.  They've got nothing else.  Except possibly early access to culture, which takes ~25 minutes to kill a homeworld (allegiance change capped at -.07/s).  And culture seems to be easily countered.

Sometimes you can't.  I think the Revelation's level 6 Provoke Hysteria needs a buff.  That's part of the point. 

Sometimes you don't have access to the seige abilities, like the Egg's level 6 yet.  Or can't build more Cap ships.  So I'd like to know what the frigate's "damage" actually is?  Annatar?  Or Kitkun?  You know?

As a rule of thumb, if I need 2-3 siege frigates, I go with siege frigates.  If I need 4 or more, I bite the bullet and buy a capital ship.  Of course, that's just a rule of thumb and there are plenty of exceptional circumstances.  As I've already implied, siege frigates are patently worthless as anything more than an expensive decoy in battle.  If you want in-combat performance, always go with a siege capital ship. 

Seeing as you're curious, I'll do a proper test to compare siege caps against siege frigs with abilities.

Okay, I only had time to do two tests:

Level 1 Vulkoras (siege platforms) vs 4 Krosovs => winner is Vulkoras... Krosovs were 1 volley from destroying the planet.

Level 1 Marza (raze planet) vs 4 Destructors => winner is Marza... again destructors were 1 volley from destroying the planet.

These tests were made with the the 10% antimatter regeneration upgrade researched to ensure "fatigue" was not an issue; both the Marza and Vulkoras kept using their specials the whole way through.  Seems pretty conclusive that siege frigates are simply outclassed in every single way by siege capital ships.  The only reason to get them is if you can't afford a new capital ship.

I don't think it is PER SHOT per se, but rather PER SALVO. I say this because the siege frigates, the Vulk, the Marza, and I think that's it have multiple siege weapons; on all TEC&Advent caps the siege weapons fire a salvo of 3 rounds.

So, along that reasoning, I believe that the damage is PER SALVO, not PER SHOT. Two very similar, but not quite the same damage applications.

Man I love OVERTIME damage on Sins guns.

Ah. I did not mean to debate semantics.

Interesting findings though. I can feel a mod coming on.

If you cannot afford a cap then the tactic I suggested above is ideal. The siege frigate is never intended to be a combat ship, so keep it out of the way. Only when you have cleared the planet of all enemy ships should you bring in your seige frigates. They can then quite happily go about bombing the planet unmolested.

A simple increase in their bombing DPS would allow those 4 seige frigates to out damage those seige Caps.

Siege frigates and Heavy Fallout are changed in 1.04 Entrenchment. We haven't decided if they will change in Sins 1.18 though.

Ooh, have to look out for those changes, but why not change them in vanilla sins as well?

Great news; glad to hear the SF is getting the attention it needs. 

Well, you have two options.  One is to run an in-game test, the other is to find all the numbers and crunch them.  Seeing as I do not know the DPS of siege platforms, an in-game test is all I can do.

I played a quick match on point blank, and finished off the enemy's homeworld with a level 3 Vulkoras (2 points platform, 1 point assault specialization).  Here were the results:

110 seconds - 1500 damage dealt
210 seconds - 3000 damage dealt
305 seconds - 4500 damage dealt
435 seconds - 6000 damage dealt

Shortly after hitting the 4500 damage mark, antimatter started becoming an issue for the Vulkoras.  So, presuming antimatter is sufficient a level 3 Vulkoras can manage almost 15 DPS in total.  Obviously a higher level Vulkoras will manage more damage than this.

Now, by comparison, Provoke Hysteria will deal 2400 damage (40%) to a 6000 hit point planet over the course of 40 seconds.  This comes out to 60 damage per second.  However, unlike the Vulkoras, it doesn't keep up a constant pace, and after dealing that 2400 damage it will go on cooldown for 180 seconds.  With that in mind, provoke hysteria averages 2400 damage over 180 seconds, which comes out to 13.3 dps.