In some cases yes you can. People refer to the different power levels of different sci fi shows to compair to other sci fi shows and so on. So like I know of a website that when a vs like scenario is talked about they take one factions energy weaponry and tech and put them up against another sci fi tech and see who has the most power levels. I don't know where they get the numbers from though.

One of the key differences between the Sins-verse and the two you've just mentioned is the way surface battles are portrayed.  In both of those universes, surface battles are exceedingly important.  In the Sins universe, they're portrayed as completely irrelevant.  This seems to indicate that orbital weapons are so powerful that anything that you could possibly build on the surface is completely harmless by comparison.  From this, I'd say that the firepower of the Sins universe is many, many orders of magnitude higher than either of those two. 

However, I'm more or less taking guesses at the meaning and abstraction behind the game mechanics here.  Take from that what you will.

I disagree- not due to fanboyism, mind you, but on the basis that the inverse might very well be true instead.

That is to say, it might be that surface weapons simply lack the firepower to harm orbital targets; the engineering simply 'hasn't caught up', so to speak. Whether this is due to an inherent limit in surface weapons emplacement designs, or, IMO more likely, sufficient enough protection equipped aboard the starships to make surface ordnance negligible.

Alternately, it might be that the dominance of orbital bombardment is due to the sheer cost of sending down surface teams, especially on an interplanetary, let alone interstellar, scale.

In the case of the former, having done a great deal of reading on the subject, I can safely say that it is impossible to determine. This is a result of the rampant inconsistency in that aspect of 40K writings. The numbers that were done up ranged from "low/medium megatons" to "high gigatons/low teratons"- and that's for the same ship class, same fittings. And also ignoring the equally rampant inconsistency WRT ship sizes of 40K.

So asking if SoaSE is on 40K level of anything is like asking a bunch of people if they like a particular thing- you're likely to get such wildly differing answers that it can be impossible to determine an aggregate 'value', if you will.

Darvin's point, which is quite logical, is that the utter dominance of orbital combat in SINS indicates that orbital-carried ordnance is far more powerful than anything that can be deployed surface-side.

In contrast, 40K has a heavy emphasis on ground warfare- often will you hear of the thousands of regiments that must be carted around the galaxy. In 40K, ground combat matters- a lot. Whilst in SINS, ground warfare is fairly irrelevant.

It's fairly logical- though it does ignore other possibilities that would assure the dominance of orbital ordnance over ground combatants; the preeminent example being cost. It's far cheaper to build bombardment ships than trying to ship the hundreds of thousands, to tens of millions (OR MORE!), soldiers you'd need for a planetary conquest.