Hi
The 3SGE celicas have the model number ST202, the GTFour is the ST205.
The 93-99 celicas are known as 6th generation celicas and have different specs based on where they were sold.
In most non-japanese markets the celicas had low powered 2.2L engines - in NZ it was know as the GS.
The Japanese domestic market (JDM) celicas had the model names SS1 SS2, SS3 and GTFour. Happily, because we are also a right hand drive country and are allowed to import japanese cars, we also get these models in NZ (from my experience the SS celicas are a lot more common than the GS's).
The SS1 had the 3SFE engine (more ecomony based)
The SS2 had the 3SGE engine
The SS3 had the 3SGE engine and from December 1997 was fitted with the 3SGE BEAMS engine.
BEAMS (Breakthrough Engine with Advanced Mechanism System) which among other engine improvements has Toyota's version of varible valve timing (VVTi) on the intake valves.
This link has good descriptions of VVTi:
http://www.toyota.com/html/help/glossary.html
A BEAMS engine is easy to identify since the BEAMs has a large red cover on the top of the engine and an emblem that says BEAMS on it - the picture in this link:
http://www5e.biglobe.ne.jp/~formura1/HP%20image/CELICA5.jpg shows the BEAMS 3SGE. This site:
http://www.toyotaparts.co.nz/celica/page7.html shows the non-beams 3SGE (SSII) and 3SFE (SSI).
I have also heard that some rare SSII's came in a BEAMS VVTi option, though I have only seen these on the web and never in real life.
There is also a 3SGE BEAMS Black Top which has Dual VVTi (intake and exhaust) which is currently found in the Altezza RS200s.
Since you've asked about the 3SGE celicas I'll focus more on them:
The SSIII is 10Kg heavier at 1210Kg than the SSII (1200Kg). SSIII's also came standard with Super Strut suspension which is Toyota's attempt at improving on the Macpherson Strut setup - Super Strut was an upgrade option in the SSII as well. It may be due to the Super Strut suspension that the SSIII's minimum turning radius is greater at 5.5 metres, compared to the SSII's 5.2 metres.
In 1996 the 6th gen celica had a facelift, with a different front bumper (where the indicators become clear and the fog lights are in their own compartments in the bumper). The rear lights also changed with the lights having a smoother all in one look and the indicators changed to clear with an orange lens.
The SSIII's appeared around late 1996 just after the facelift of the 6gc and from late 1997 on most have the Projector Headlights as standard equipment.
The SSIII reportedly consumes 10% (approx) less fuel (VVTi more economical?) and the SSIII interior was updated a little with new fabric design on the seats and doors (with a red fleck instead of blue?) and some SSIIIs had the 'White gauges with Orange needle' option installed. There are also some SSIIIs with a lighter, silvery colour on the centre front console (around where the stereo is).
Externally, SSIIIs can also come with an uprated spoiler package (this maybe what some dealers are calling the aero spec) including side skirts and front & rear bumper extensions and spoiler posts raising the rear spoiler up just like a GTFOUR, except they had an SSIII badge on them.
The celica handbook info on the SSIII:
General Info:
Length: 4505mm (177.36 inches)
Width: 1750mm (68.9 inches)
Height: 1305mm (51.38 inches)
Weight: 1210Kg (2668 pounds)
Minimum Turning Radius: 5.5m
Engine Model: 3S-GE VVT-i
Engine Type: Straight (inline) 4 Cylinder DOHC 16 Valve
Displacement: 1998cc
Max Power: 200ps/7000rpm (which is 197hp/147kw according to this site:
http://www.mr2ownersclub.com/converter.htm)
Max Torque: 21.0kg.m/6000rpm
0-100 km/h ~ < 8.1s (since a non-BEAMs SSII's time is 8.1 - based on this site:
http://linjin.mine.nu/celica.htm )
Compression: 11.0:1
Fuel System: EFI (Electronic fuel injection system)
Fuel Tank Capacity: 60L
Fuel Type: Premium Unleaded (100 RON)
Steering: Engine speed-sensing variable-assist power rack-and-pinion
Engine Oil Capacity: 4.0L (4.5L with filter replacement)
Coolant Capacity: 6.9L
These are pics of the SSIII with the projector headlights, optional spoiler pack including side skirts, front and rear bumper extensions (splitters) and the raised rear spoiler:
Hope this helps.