3 Ton A/C for 1096 sq. ft. cinder block home?

I have a house that is made completely of cinder block (even interior walls). I also have single pane windows and a metal roof with no insulation what so ever. It is a open floor plan 2 bedroom home. My question is that I had a 2 ton unit that went out last week and the HVAC gentleman said a 2.5 ton would work but really suggested a 3 ton. The 3 ton is $1000 more and I really want to be sure that I have the most efficient A/C for my size house and building materials. Humidity tends to build quite a bit because of the st up. I like to trust the professionals but don't think it hurts to get a second opinion. Thank you all. Note: it is a dry air unit, whatever that means.