Will I still be relevant at top consulting firms with a < 3.5 GPA?

I'd say you have a 19% chance if you interview on a Tuesday.

If it's a Wednesday and raining then you're looking at more of a 14.88% chance.

The trick is to lead into your intro with the U.S. News and World Report rankings. There's a whole lot of other ranking metrics out there, but if you drop U.S. News by name to a McKinsey partner they'll be asking you when you can start.

You're thinking about this question the wrong way. The issue here isn't that you have a GPA slightly below 3.5 (you can always round up). Instead, the real issue is that that any GPA below 3.7-ish is already suboptimal for MBB recruiting. Top consulting firms have a reputation for being sticklers regarding this sort of thing, and it's even worse for junior internship recruiting, since consulting firms take relatively few summer interns compared to... say, bulge-bracket investment banks.

That being said, it's still entirely possible for you to get interviewed at MBB. You'll just need an existing consultant to refer you-- that's where networking comes in. However, going to college networking nights is not enough. You need to follow up with the people you meet at these events, and have one-on-one conversations with them afterwards, either over the phone or in person. Consultants at college networking nights will meet dozens of people over the course of the event, and it's unlikely that they'll remember anyone in particular. On the other hand, if you speak with a whole bunch of alumni/current consultants one-and-one, eventually, one of them might like you enough to pass your resume along. That's what you're aiming for.

As an aside, this is true about all networking in general. Personally, I found nearly all of the networking nights at my college to be largely pointless, as I could've just individually reached out to all of those people beforehand and achieved much better results.

And if things don't work out for you this coming year, then work hard and boost your GPA for full-time recruiting instead. At the undergraduate level, MBB hires nearly as many students in the senior full-time recruiting process as they do in the junior internship recruiting process.

I'm an analyst at a MBB and involved in recruiting. I would definitely recommend for you to do some networking in order to get an interview. I lead recruiting for a T15 private school and we look for candidates that are in the 3.8 GPA range (maybe 3.7 for engineers). If you can somehow talk to a partner and get him to refer you or put in a strong word for you, then you'll be set for an interview. It's entirely possible and I know people with lower GPA's than you that have gotten offers/interviews, but the lower your qualifications, the more you have to network. Also, having a solid summer internship would help your odds.