Hi Antoni,
Besides what you mentioned being the length, the STK is 2' longer, and weight, the GTK is 11 grams lighter, the GTK has a max casting weight of 130grams, the shorter length perhaps enabling it to handle slightly heavier lures on the top end, where the STK max recommended weight is 120 grams.
Both rods are rated up to PE 5, and a max drag of 7 kilos, with the GTK having a recommended fighting drag of 4 kilos, and the STK at 5 Kilos.
Otherwise I believe the rods are of similar performance, but with about $100USD difference in price.
Hope this helps..