Before the 1940s or so most young US Jews still spoke Yiddish and barely spoke English.

You could probably say the same thing about early 20th century immigrants from Germany or Scandinavia that scored better than Jews of that era in intelligence tests.

tests on Jews are small in number in general because Jews are a fraction of the population

Actually there seems to be quite a bit of testing data on Israelis, and if I remember right earlier tests on Jews in the US from sources like Ellis Island and US Army intelligence tests, and none show particularly high scores. The issue is that the sample sizes used to make conclusions about high Jewish IQ in some books are absurdly small, like the often cited study of 59 from a Jewish private school used by people like Charles Murray. Generally speaking, the larger the sample size, the lower the IQ scores we see on the subject.

Israel is not full of Ashkenazis

1/3 of the country. That's a pretty significant amount, enough that one would expect Israeli average IQ to be significantly higher than it is if global Ashkenazi IQ was as high as some say.

2) Many so-called "Ashkenazis" are probably gentiles who tried to escape the soviet union

I have a hard time believing the most fanatical of Jews(Israelis) would get rolled like that by opportunistic Russian goys. I'm not saying it never happened at all, but the numbers are likely very small, although to be fair I suspect a lot of ashkenazi Jews worldwide have very little Semitic blood, and are primarily just whites that call themselves Jews.

There is no reason given for why this is implausible

Maybe not implausible so much as unlikely. Especially when were talking about a global population residing in isolation from each other for centuries in very different countries and circumstances being claimed to have uniformly developed higher IQ. I suspect there ARE pockets that did do this, but others that didnt at all.

1).We don't know for sure how much smarter Ashkenazi Jews are relative to White Gentiles (but we know they are at least somewhat smarter, 5-12 points, I say 110)

I say we dont KNOW this. There is some evidence that may be the case, and some that its not. Without large representative test samples from objective sources there's no way to know, and we dont really have those, but as pointed out the larger the samples the more average ashkenazi IQ seems to be.

2) And even the most generous assumptions on Ashkenazi IQ cannot explain their power

You don't need to make any allegations of fakery or whatever to show this. Their overrepresentation still has to be due to "something else" - and it's up to denialists to prove it isn't what it obviously is

I personally dont really care that much about the IQ issue, because most of the overrepresentation occurs in areas where it absolutely should not exist regardless. No one should ever tolerate such a tiny group completely dominating their media for such a long time regardless of how "smart" this group claims to be. That it has occurred explains a lot of the clownworld shit we see today.

In so far as it matters, if I had to place odds on what the reality is, I would say it's probable American Jews have a little higher average IQ, say around 107, owing exclusively to higher verbal IQ, with global ashkenazi IQ a little lower, BUT there were probably historically pockets of ashkenazis that were substantially higher. I also suspect ashkenazi IQ is decreasing in recent times due to numerous factors, including that the supposed selective pressures that gave rise to this alleged higher IQ havent been present in quite some time, and ashkenazis have increasingly intermarried with Sephardic and Mizrahi Jews.

I think IQ tests are primarily just good at testing your ability at taking IQ tests, and are more influenced by environment than many of their proponents claim, but that's a whole different discussion.