I preferred Overclocked to IV, both in story and characters, but they're both fun. Like Soriku said, Overclocked isn't a traditional tactical RPG, it's more like a standard RPG with a grid map and skills.

Though, if you only want a traditional RPG, then you'd probably prefer IV.

Is overclocked worth it if I already have normal Devil Survivor?

Some people say yes, some people say no.

If you love the game, yes. There is extra content added, however some say it isn't enough.

Record Breaker though is 100% worth it if you have the original because it's essentially two games in one. (there are two arcs, two separate stories completely different from each other)

I haven't played the original, but when overclocked was first released, there didn't seem to be enough to be worth rebuying it. Two separate story arcs would have caught my attention earlier. Everything I read is that there is an extra day for certain routes/characters but it was largely inconsequential.

If you've played the DS game, I'd say it's problably not worth it. I only played the remake, but from what I've read, the only story additions was an 8th day for three of the routes I believe. I only did Yuzu's route, and the 8th day content probably took an extra ten hours, with a fair chunk of that being grinding against new demons.

I wouldn't say it's a bad deal on sale...but if you already played it, the extra content won't seem very substantial.