Hello

As you have mentioned your category is OBC and with 511 GATE Score there is a chance of getting New IITs like IIT Bhubaneshwar, IIT Indore , IIT Patna, IIT(ISM) Dhanbad, etc. But you can apply for some old IITs  like IIT Roorkee, IIT Kharagpur, etc till spot round because there is a chance of getting that.

For NITs there is a chance of getting not best butbsome good NITs like VNIT Nagpur, NIT Durgapur, NIT Bhopal,etc. Try CCMT till last round to get your top priority.