I have been lifting 4x5 rounds of hay with my
L3400 with the LA463 loader which has about ~100 lb less lift capacity than your loader just fine. It handles them like a champ and I expect yours will as well.
I can lift bales in the middle of the winter to full height if necessary but generally don't need to do this. The highest I go is to to put them into the round bale feeder.
Where I do have difficulty is getting the second stack of bales off a semi.
If I needed to, I could stack them two high but anything higher than that gets difficult.
I have R4s filled with Calcium Chloride and always have something on my 3PT like my 600 or so lb snow blower. If you have Ag's which can hold less fluid, I would recommend some wheel weights in addition to the fluid.
My
L3400 has handled EVERYTHING I have thrown at it like a champ. About the only thing it could not lift was my 2500 lb cattle chute
Now all of this said, if I had known I'd be handling round bales when I bought mine I would have stepped up to the GL3240 (GL3130 was around back then) or the GL3540 JUST so that I could have gotten the LA724 loader.
Now is the time for you to make a change like this if you would like to.
If you are handling occasional 4x5s, you are going to be perfectly fine. Last year I fed about 60 bales.
You won't regret an upgrade to a bigger loader however - I'm pretty sure of that. However you don't have to be worried with your current choice IMHO.