sargent E-5
Specialist is a rank - Pay Grade E-4 - which is classed as lower enlisted. Pay is equal to that of a Corporal, but Corporal is the higher rank of the two (Corporal is a noncommissioned officer rank, Specialist is not).
major is a higher rank than sargeant rank.
There isn't a specific rank attributed to it. Generally, a tank gunner would be Private (E1) through Specialist (E4). Field Artillery would be more the same. There is a Gunnery Sargeant in the Marines.
Specialist 5 - it's a discontinued Army rank. A Specialist got the same pay as a Sergeant (also pay grade E5), but was not a noncommissioned officer.
SPC is the abbreviation for Specialist. Currently, there is only one grade of Specialist - E4. Specialist grades used to go all the way up to E9 (although the Specialist 9 or SP9 was only theoretical - nobody had ever actually been awarded that rank). At that time, the E4 Specialist was abbreviated as SP4. However, all the Specialist grades above E4 have since been done away with, so there was no need to indicate the pay grade with the rank, thus the abbreviation became SPC.
SARGEANT
There is no Specialist Eighth Class in the US Army or Marines. Most specialist ranks were phased out in the 1980's. Specialist Fourth Class (Spec 4), paygrade E-4 is still awarded in the US Army for some MOS's.
The rank of Sargeant has the insignia of three downward-pointing chevrons.
You start out with a higher rank and higher pay grade.
In the US Army that is the rank of Corporal or Specialist. In the US Navy that is the rank of Petty Officer 3rd Class. In the US Marine Corps that is the rank of Lance Corporal. In the US Air Force that is the rank of Senior Airman.
anthracite
Petty Officer 3rd Class. Pay grade E-4, equivalent to an Army Specialist 4.