It isn't 33k/day. However it is something similar. I noticed that the log entries (simul game) show discrete amounts being converted. Going by memory here, I believe that a RC III will convert in 50k -> 35k batches several times throughout the turn (that's the 70% conversion rate).
Yes, it maxxes out somewhere around 1M/turn due to running out of time during the turn. Yes, this is possible in large games even if you aren't a total economic idiot. I've been in games where I captured several planets from an organic player and had a massive surplus of organics - perfect for converting. I've also been in games where some of my big resource producing planets and/or spaceports were glassed/captured - this can bring your construction efforts to a halt in 1 turn. A Resource Converter is a must for any empire. As mentioned before having a backup is a great idea since they can't be built in one turn normally. Also if you end up converting > 1M/turn, they both can work together.
edit: A RC on "repeat orders" won't try to convert multiple times per turn; just once per turn. *BUT* the order will stay in the queue and it will try to convert *EVERY* turn. If you give another conversion order to the RC, this will be added to the order queue and it will attempt to do *BOTH* every turn. I once made this mistake also while converting org to min, didn't notice what was happening, but noticed that my orgs were going down and now I had a surplus of mins. You guessed it. I converted min to orgs. That means that each turn I was converting org to min back to org again, each time losing 30% until I figured it out.