Only load calculations would tell.
Why not spend the money once and correct the conditions than spend the money monthly trying to compensate?

 

She’s had the right idea but something you need to understand is load calculations are based on whatever the outside design temperature is and 75 for an inside design temperature. It sounds like your present system will hold 75 under most conditions you see so it is sized correctly from the information you provided.
As ehsx stated money is better spent upgrading the structure rather than upsizing equipment. The other thing you need to know is too big of equipment will not have to run as long so humidity will become a problem. Thus could even happen with your current equipment if the envelope gets too tight.

 

Larger equipment requires more air flow, often involving duct improvements. Increasing equipment size by 50% means 50% more air flow is needed.

Air VOLUME is the term you’re looking for, not velocity.

Improving the house makes much more sense than getting bigger equipment. Bigger equipment will use more energy to compensate for the house leaks.

 

In theory perfect. In reality there are other issues the other 90% of the time that room does not get sun.

Tighten the envelope, seal the leaks, slight positive pressure with outside air the issue goes away

 

So, a 3 ton system removes more heat from air. so outlet air is colder?

No. A 2 ton and a 3 ton system (properly installed) will both produce similar outlet air temps. The tonnage is a measure of capacity. A higher tonnage unit can cool a larger area than a smaller

or there is ”more” cold air?

Sort of...higher tonnage requires more airflow so the volume of air is increased

higher air velocity?

Higher tonnage means more volume, but the velocity is the same (typically 350-400 cfm per ton). Larger units don't move air faster, they move more air

as in more cold air?

Yes, but not for the reasons you think and only if the larger unit has the appropriate size ductwork attached.

can a higher cap system, say 3 ton achieve 71f at all times?

Possibly, or it could be oversized. Too big is a problem too - it will cycle a lot, be inefficient, and won't remove humidity as well. It might be cheaper and more effective to improve the insulation, add some shade trees, upgrade windows, maybe even add zoning.

 

You skipped 2.5 tons as a option, as even some inverters come in .5 ton increment sizes..

 

3-Ton BOSCH

Now you can dial it to whatever you want