my orange cat who i keep an eye on due to him still being on over weight side can go up to 149 within hour of eating low carb 'dry' food, often he is more in the 120 range within 1-2hrs after eating though (using pet meter). his non-food BG's are always in 70's like rest of my non-diabetic cats. the one time i tested others not too long after eating low carb dry food in the past, they were all around 90-100 if i recall right.
not every cat is the same but, from what i observed with my diabetic tux, 25 points seems to be the average low carb dry food will make his BG rise by. with wet food, even though all low carbs, some do nothing and some raise it just a tad bit.