No score is safe enough. Last year the cutoff went exceptionally high as compared to pervious years. So, marks cannot be a parameter. But since you asked, you have to get above 78-80 in GATE exam for things to materialise. Other factors like normalisation etc. also constrain the prediction.
To get into any PSU, a rank above 300 is safe. For rank up to 500 you can get a good branch in IITs.Best of luck. Go, kill !