Seeking advice on CMP M1 Classifications

I've read the descriptions for Field, Rack, Service and Special grade on the CMP website, but I'm looking for persons with 1st hand knowledge of what you get for your money.

If you were buying a CMP M1, would you purchase a:

Field Grade for $650

Field Grade for $950 (guaranteed to be IHC receiver)

Service Grade for $750

Special Grade for $1050 (competely refurbished rifle)

Special Rack Grade for $700 (partially refurbished WRA receiver - Heavy Pitting above wood line)

Special Rack Grade for $650 (partially refurbished ??? receiver - Heavy Pitting above wood line)

Also, I'm trying to figure out if higher or lower numbers are better for muzzle and throat erosion.