engine wise, there is no difference. exterior and interior there is. like the tail lights on a gti are smoked and unless you have a k2 or gt jetta, they arent. as for interior. they have dif. gauges and dif. seats unless like i said you have a gt or k2 edition. im sure there are other thinks. like shift knobs and stereo and stuff but thats all i can think of right now.
So what you're saying is that the 1993 2.0 Vento(Jetta)GL has the same power output as the GTi of the same year at least as far as the gearbox? My Vento has the Auto-box whereas most GTi's in the UK have manual transmissions.
im pretty sure the gti has a closer ratio gear box. i think it has to do with the car type. a sedan is going to be more family oriented whereas the hatchback 2 door is gonna be the racy like car and the performance difference shoudl show.