60 should be enough, but you'll be close to its full capacity, so i'll go with the 140 in case you want to download demos or more games in that hard drive.
I agree with this post. Remember, all game data is stored on your PS3. That includes, but not limited to, Save data, Fragmentation data, Utility data, Blu-ray data, Demos, PSN content: Wall paper, music, PS1 games, etc., and things of this nature that I have yet to mention (pictures, music, updates, and so on).
When you add the fact that FFXIV will have you download many and many more updates, you will reach capacity probably pretty quick. Unless, I hope, they override most of the previously downloaded data to make way for the new one but add in you DLC and you're maxed. If you're thinking like I am, as a FFXI vet too, you want to make FFXIV your new home. If they make this game as good as we hope, just think of all the stuff you downloaded for FFXI or bought... Yeah, that's a lot of extra HDD space you need. SO, I would go with the 140 if you can handle it. I have a 120 and am almost at max with game data alone.