Haven't used Logic Pro X but the ones in Logic Pro 9 is pretty shit imo. I don't think their are any major difference but you should check out youtube for demos since their are a lot of them out there.
Logic Pro sims are usable IMO and from what I can tell they did upgrade them in x but I'd look it up. I love logic and would get x either way. You can always use 3rd party sims.
In my experience with Logic's amp sims. They are really good for clean tones, I even prefer the Logic cleans over Pod Farm *gasp*, but not any high quality high gain heads. I guess you could always just buy a couple from Apple and see how good they are