I personally would ask him how many of these variable speed units specifically has he installed, because it sounds as though he doesn't fully understand or appreciate them.

Forget about the fact that generally oversizing the air handler above 1/2 ton (especially without mention of an expansion valve) might mean potential future compressor failure. Better yet, I personally would get a quote from another dealer.

If you are worried about dehumidification, get a whole house dehumidifier. Although my aunt in Florida has a 3-ton Greenspeed and has found no need for dehumidification with these variable speed units.

The contractor wants to install a 3 ton condenser to cool a 3800 sq. ft. house? I am skeptical about the sizes. What is your location? What area of the house does the 3800 sq. ft. include?

It is common to install a coil larger than the condenser as long as it as valid AHRI match. Ask the contractor to provide all model numbers and the corresponding AHRI certificate number. This will confirm whether is a valid equipment match.

There is a debate among HVAC pros whether a bigger coil improves humidity removal or not. I have over sized coils with my Carrier Infinity AC condensers and I found it works very well.

I wouldn't worry too much about the condenser/coill size difference. Just make sure he did a "Manual J" estimation of heating and cooling needs (as opposed to a Billy Bob's freebie HVAC calculator spreadsheet that divides sq ft by 600 and then adds a ton)! Unless you are in a very mild climate and/or have a super well insulated home, 3 tons may be a little skimpy.