I doubt ROTS will get too close to Titanic's whopping $600,788,188. I think it's got an outside chance of reaching the #2 spot, ahead of the original Star Wars' $460,998,007, but I'd still be (pleasantly) surprised if it managed that, to be honest...
I'd love to see it hit the $400 million mark for starters. Then we'll take it from there. It's currently sitting at $182,710,278 through yesterday, which is the biggest first 6 days for a movie in history. Needs $9.375 million today to pass Spiderman 2 for biggest first week ever. Probably gonna fall short though, unfortunately.
This upcoming weekend will likely be a good barometer to forecast it's overall earning potential though. It'll need another HUGE weekend, and some serious staying power to really crack the Top 5. I'm definitely rooting ROTS on though!