Most people equate 98 RON with 93 to 94 R+M/2. This isn't necessarily correct for all fuels, but it's probably close.
I used to run 93 in my stock '80 turbo, with no problems. Now, all I can get in this area is 91. I had the timing backed off about 4 degrees and all is well again.
If you can get 93 from a reputable source, you're probably fine. If you buy your gas at whatever station is cheapest at the time, I'd suggest backing the timing off a little, as I've seen lower octane gas sold from the higher octane pumps, once or twice. Yes, it's against the law but there are a few dirtbags out there.
If you are stuck with alcohol in your gas, or the other (reformulated) crap, I'd also adjust the timing. You won't notice a big drop in performance.
As others have said, a can or two of octane booster will do nothing useful for you.