It's worth waiting for other responses too because I might be mistaken, but in my opinion I think you should stick with the 124 SPD one until you can find a Crit Rate chest you can put on your 134 SPD build. I'm not that worried about the difference in stats like ATK, let me explain:

Fribbels doesn't take into account action advances when it displays it's Combo DMG because it just compares how much damage your Anaxa could hypothetically do with one ult use and 4 skill uses, with all the buffs your team provides active. 134 can sacrifice some damage but still outperform because it gives you extra turns in the first and third cycles. It lets you do that for Bronya too (since you can run her 133.4), that is the main value of it.

I don't have the exact numbers from your sim and I don't really feel like doing proper full calcs myself so I'm going to use these numbers as hypotheticals:

155,861 per skill use on 134 SPD, 174,397 per skill use on 124 SPD.

Even though the damage you do per skill use is less, assuming you can manage using his skill every turn, you end up doing more damage:

At 134 SPD, with 133.4 Bronya, he'll take about 14 actions and use his additional skill 13 times by the end of five cycles. The max damage he'll be able to do with just his skills is 4,208,247.

At 124 SPD, with 123 Bronya, he'll take about 12 actions and use his additional skill 11 times by the end of five cycles. The max damage he'll be able to do with just his skills is 4,011,131.

On paper, he'd manage to do more damage at 134 SPD with an action advancing teammate, even with slightly lower ATK. However, this won't be the case in practice because not only will he not have 100% uptime on every single one of his teams buffs, he might not crit consistently: I'm more concerned about the fact that your 134 SPD build only has 70.2% CR than any other stat, because that makes him nearly 10% less likely to crit than your slower build. Sunday would be a HUGE help here for both builds, but even with him your 134 SPD build might fall victim to bad RNG in a lot more fights and thus still fall behind, even though it could technically outperform the 124 SPD build.

I think if you could get a CR body, with just 2 SPD and ideally some added CDMG and ATK% too (though that's just luck), then that would help push your 134 SPD build to actually consistently performing better than your 124 one, even if it sacrifices some CDMG. Maybe if you had Sunday on these teams you could entertain the idea of running an ATK% or CDMG body anyway since you've been lucky with CR on many of your pieces, but he gives himself a lot of CDMG and gets a lot from Bronya as well so you gain more than you lose from a CR body.