Yeah, some cards can clock much better than others - there's no minimum other than what EVGA guarantees with their listed clock speeds. And overclocking on air reduces the max that a card can do.
I'd suggest increasing GPU core clock speed by +25 and testing in a heavy program (preferably looping it for at least 5 minutes for stability checks) - like 3DMark Port Royal (raytracing taxes the GPU more).
For VRAM, the 2080 super cards actually have chips that can (usually) be pushed really high. Try a +500 to start with and test *after* you've found a good GPU core overclock. Increments of +50 MHz and test if you are looking for more. (mine did +1250, but every card is different and some benchmarks didn't like that, so I had to drop it down to +1000). For what it's worth, VRAM clock speeds increase FPS a lot less than your GPU clock speed overclocks do.