Some of The 5 IITS first of all are IIT BOMBAY, IIT KHADAGPUR, IIT DELHI, IIT MADRAS, etc. To get s good branch ie CS and IT in these IITs obviously you need some ranks closer to 250 and below which is really competitive. And to be a part of iits, I guess any rank upto 2000 will do. Because Aerospace engineering closing rank cutoff in IIT BOMBAY was 2053 Rank.

Check the cutoffs of different branches of enggineering in IIT BOMBAY -

https://engineering.careers360.com/articles/jee-advanced-cutoff-for-iit-bombay

Best wishes. Thank you.