Hi JD 3520,
The 300CX is "approved" for round bales--SMALL bales, and is capable of lifting them--someone did some real-world testing with one hooked up on a 990, and (bale) weight-wise it's not an issue. Do a search for 990.
2900 #'s is not a very heavy tractor for the hp & lift capacities the 3x20 is offering... for maxed-out loader work it is not (and I have one) a big enough tractor to travel far, on grades, or over rough terrain & make me feel I'm not asking a lot out of the front axle.
Massive counter-weighting on the 3 pt would be necessary for regular work with them, even more if you are considering stacking them.
As far as the 300X goes... it is a less robust loader
You can get a 3 pt spear without the fear of "nose-diving", but again, it's a low weight and stacking is not an option