wow..
okay... where do I start???
90-93 is fifth gen
94-98 is sixth gen
fifth gen offered ST, GT, GTS, Alltrac(gt4)
ST was trimmed down model
GT sportier, same engine as GTS (5S-FE 2.2L)
GTS same as GT, but with widebody
Alltrac turbocharged and intercooled, AWD
Sixth gens we got:
ST and GT .. There were GT-Four(alltrac) but we never got them in the U.S.
The GTS isn't turbocharged.
going back to the hatch question, I can't recall exactly, but basically, GT hatch/coupe, ST coupe/hatch?, GTS hatch, Alltrac hatch....
trying to answer in some order...
Yes the gt4 burns the crap out of a lotta stuff.

not similar engines. Only Alltrac got the 3S-GTE (turbo/awd) layout. All else is FWD, naturally aspirated, usually 2.2 L. 4th gens were 2.0 L . THere are also some 1.6 liter in the 6th gen.. whew..
hope this helps,
I'll get some links together for you and put them on my webpage sometime..
There are plenty of 'History of' pages out there, I'll see what I can do.
later,
CHris
http://way.to/celica.gtfour