This is a theory of mine based partially on Cell's statement of his own power in Super Perfect Form (Which can be considered hyperbole to a degree). I will also delve into more POSSIBLE feats.
Based on how Gohan was either equal to or stronger than Super Perfect Cell I will proceed to try and make calculations on the power level It MIGHT take to destroy the solar system.
First let's compare Goku and Gohan during the Cell games. Aside from Super Saiyan 2, I believe it is reasonable to assume that they were essentially equal at the time. Second let's determine their power levels at the time by looking at it like this. Goku during the Frieza saga was at a level of 150,000,000 for Super Saiyan, based on MOSTLY reliable sources.
During the Cell games, I am quite positive that Goku in his base would obliterate Frieza in the same way. Basically I'm saying he's stronger than Frieza at his base during the Cell games. He might be at the same level his Super Saiyan form was at the Frieza saga, or he might be stronger. But either way, for the sake of simplicity, we will use 150,000,000 for the base level at the Cell games.
Thus we know that 150,000,000 is his base then. If we give that base a Super Saiyan multiplier of 50 then we get 7,500,000,000. Now let's look at Super Saiyan 2 which is supposedly a double of the regular. So it's going to be 150,000,000x100. And we get 15,000,000,000.
Thus based on how similar Gohan was to Goku at the time we can say that Super Saiyan 2 Gohan was also 15,000,000,000. And Super Perfect Cell was pretty much the same. Or he might have been a little higher or lower. But if we accept what he said and believe that he could destroy the solar system, then we could say that the minimum for solar system busting is 15,000,000,000.
Now before anyone says anything about him not being able to do that look at it like this. Sure, Cell seems like he wouldn't be able to create a Kamehameha big enough to blow up the solar system. But that doesn't mean he doesn't posses the raw power to do so. And why would he anyways? It would waste time for him and waste power.
If you look at how Vegeta during the Saiyan saga (Who we can assume has had experience with blowing up planets. Not based on filler but just fighting experience) then we can say that 18,000 can level a planet. Light years away from Super Perfect Cell's power level In this theory. And before anyone says he only blows up the core then look at how easily Piccolo blew up the moon and even Master Roshi. If they could do that to the moon (Just turn it to dust in an instant) with power levels ranging from 126-400 then blowing up the mass of the planet would not be far fetched at all for 18,000 as a power level (18,000 is essentially 45 moons and the Earth I believe is actually slightly lower than that). And Vegeta was pretty confident that there would be nothing left. And if Vegeta couldn't breath in space then he wouldn't risk blowing away his own space ship. So I am sure it wasn't just the core.
Now if we look at Saiyan saga Vegeta and compare him to Super Perfect Cell then we can assume that blowing up a Solar system is not far fetched at all (Based on this theory). For Super Perfect Cell we could also assume that he can blow up approximately 833,333 planets all massed together. And if anything, he is a master of Ki control. It doesn't take a high power level to control Ki in different ways. It just takes a high power level to make it an effective attack. Not every attack the size of a planet will always have the power to blow it up. So it's easy to assume that Super Perfect Cell can create an attack that could spread from towards a solar system.
A problem with that though is that we could also assume he can level a galaxy, but only if we include Broly into this. For me I kinda do include him since it technically did take place in a point of time in the series during movie 8. It took place during the 10 day wait for the Cell games. And I usually tend to think that Broly at the time was SS2 equivalent in his legendary Super Saiyan form. Which would explain why not even 2 Semi-Fully mastered Super Saiyans, 2 Ascended Super Saiyans, and 1 Super Namek couldn't do so much as even scratch the ugly bastard. But this is just my theory on Broly's strength. And I am one to usually come up with and partially believe more than one theory.
As for Bills (The god of destruction from the recent DBZ movie) I would assume he is far more capable of busting even more.
Super Saiyan 3 Goku was a flea compared to Bills. And I am positive that SS3 Goku at the end of Z was (Pre-time skip) far capable of leveling a solar system if not a galaxy. And Bills put him down with a tiny minuscule flick to the forhead and a miniscule tap to the neck. And before anyone says he used pressure points, then he would have used such a technique against Goku in his god mode. But he didn't. And don't tell me he didn't because he wanted someone worthy. If Bills was SKILLED enough to put Goku down even in his god mode with those moves then he wouldn't have thought Goku was worthy. Bills took SS3 down with brute force. And made him look like the worlds weakest bitch. SS3 fails in comparison to Bills power. No special technique was used. Period.
So Bills could technically be classified as a casual solar system buster. Maybe even a galaxy buster. Maybe a universe buster (If we over analyze everything). But we don't know. All we know is that he is light years ahead of what Super Perfect Cell is capable of. In the movie it was stated that even if Goku trained for a million years, his SS3 still wouldn't match up to Bills. He had to fight in his god mode. So Bills is also pretty much a billion light years away from Cell in both power and destructive capability.
I hope you found this theory interesting. I always find it fun to analyze these things.