Heat Pump-Air Handler question

I have a 12 year old Bryant Heat Pump, 10 Seer, 3.5 ton. The reversing valve is crap. Right now I am running the heat in Emergency mode (electric furnace) until I fix it.

Ive been on www.ingramsairandwater.com and located a 13 SEER 3.5 ton Goodman unit with matching air handler. My question: is it reasonable to go with same 3.5 ton system I had before without going to all the trouble to do a load calc on the house if I am getting the air handler with the variable speed fan? Wouldn't the variable fan speed settings allow me to program the desirable cfm moving through the house.

Thanks for any advice

Jfls45

Without running some calculations, it's impossible to say, but 3.5T would heat and cool a quite large house. In the summer, was the humidity level in the house comfortable? If it got cold, but it was still clammy, that's an indication that the unit is oversized. A variable speed air handler helps, but that can't overcome an oversized unit's short cycling if it is oversized.