i'm with skycaptain on this one. I've met, flown with, and trained guys who have more "natural" stick and rudder ability than others, myself included. I've always considered myself to be a competent aviator, intelligent, and pretty poised with thinking myself through a situation, and in the other side of my mind, i think "You're not bad, but you're not the best stick in the world". I think it's only natural to wonder if a person is "ready" for the 121 world, and it's good to have the question, shows that you're doing some self evaluation, looking in the site and getting feedback from others (especially those already involved in the industry you're intending on joining) also shows some good judgment.
Do i think that every pilot out there with 220/25 me is going to rock it out in the jet? NO, do i even think that the vast majority of pilots out there with that experience level are ready for the jet? NO....only reason i say that is when i was instructing individuals with 220hrs, they were having a hard enough time getting a lazy eight done to standards. Now i know that flying a CRJ/ERJ isn't the same as doing commercial maneuvers, but the point would be if you can't show mastery of control of the skychicken, what makes you think you'll be able to show mastery of control in the jet...
On a different note, the only time having the "low time pilot" in the right seat of the RJ is really going to make a rather large difference is when the situation is an emergency or "abnormal" and the captain is either mediocre, unsafe, or incompetent, by the time the LTP has enough time to feel comfortable in the airplane, he'll most likely be just as safe as the guy with 1500-2000 TT. Another thought, if you're in an emergency situation, with a lackluster captain, would you rather have a guy next to him who's flown single pilot night cargo for 3 years, or a pilot factory graduate? Whether it'd actually make a difference or not, eh, u can choose.