Ops Consulting to IBD - Renege on Lateral Offer?

long time lurker, first time poster.

background - Graduated in 2017 from a top non-Ivy UG target. Did my SA in a lower-bulge coverage group and didn't get a return - ended up going to operations-heavy management consulting with plans to go back into IBD.

Started recruiting after Thanksgiving for banking offers and ended up getting one with a no-name boutique (3-4 man shop) with an extremely short timeframe to accept. It's a real analyst offer (pay is fine, it's not an internship, I'll get sponsorship for my FINRA licenses) and the experience may well be pretty good, but absolutely zero name recognition. Not wanting to push my luck, I accepted it.

Fast forward to today - got a superday with a top tier 3/lower tier 2 MM boutique (think Houlihan coverage level of prestige - definitely a big step up in name recognition but still pretty far from the top of the table).

Would like some input on the following things:
-I'll do the superday with the larger MM, but should I tell them that I have already accepted and plan on reneging in the interview? Should I tell them the name of the no-name? (I have yet to). If I get the offer, should I tell them that I plan on reneging before I accept?
-The no-name knows the name of the tier 2/3 MM that I'm doing the superday with - they don't know it's that one in particular (I gave a few names in my interview) or which coverage vertical I'd be going to. What kind of risk profile am I looking at?
-Is the prestige bump worth it from a career advancement/exit op perspective? Pay difference is essentially moot to me, and given the better hours at the no-name it's a wash in that regard. I'm shooting for pre-MBA MM/LMM PE or maybe something in corp dev (not shooting for megafund) - if it's gonna be similarly tough either way I'm not gonna bother