That's right. I don't think there is something else that you can do about it. Lowering the stack of MUI is, afaik, irrelevant as this only afects the memory consumption of the MUI preference program, not MUI itself.
Another thing that you could try is too fall back to older external MUI classes which requires less memory but they may be buggy or many clients might require newer ones.
In any way, web browsing with only 4MB of fast-ram... is not enough no matter what you do.
