You'll be close on payload as the 575 dry tongue will be around 900-1000 in reality. Dont shy away because of that alone.
The length difference is more significant. The 28 model is probably 32' bumper to ball which can be very challenging for many State Park sites. And more challenging if this is your first TT.
Travel with a longer enclosed trailer is also more susceptible to wind effects. Time and time again, people do not feel stable towing that length trailer with a 1/2 ton without a Hensley or Propride hitch. They are expensive, but worth their weight when towing. Trust me! Or heck....any current user of them.
If you dont plan on spending actual living hours within and doing active State Park trips where you really only sleep in the unit except when its raining, then I'd go with the 24 hands down.
I speak reality having gone thru this exact experience, coming from a 23' TT and now having a 28' (32' total). We miss the 23' for general travel but love the 28 because we also use it as a living space (practically a 2nd home) far often more than we travel. The decision was practically made for us based on our actual use of the TT. So keep it real!