Yes, but it can't climb that high with a full bomb load, as pointed out in another thread (I think, it might be in this one, but while back). And unless it has a higher celing than any other plane then its not unstopable. Its just difficult, same as with the 262.
And unless I completly forgot what the 262's speed at its max alt, then 400 wouldn't be enough to outrun it, and, again unless i forgot what the A/C's top speed was, the B-29's speed was below 400.