while( nTrianglesDrawn < nTriangleBudget ){
GetWorstTriangleFromPQueue();
SplitItAndInsertChildrenInPQueue();
}

However, you have stated that you don't try to converge on the desired triangle count by adjusting the error; in that case, you don't need a priority queue, right? You just need, say, a stack or a queue, to store triangles:

fErrorForNextFrame = MagicalFormula(fErrorForLastFrame, nTrianglesDrawnInLastFrame);
while( StackNotEmpty() ) {
PopTriangleFromStack();
if( triangle.error > fErrorForNextFrame ){
split(triangle); // pushes children in stack
} else {
DrawTriangle();
nTrianglesInThisFrame++;
}
}

I just hit me that I do the expensive priority queue without actually needing it...

btw the TreadMarksDemo2 kicks so much ass...
everyone I show it is wowed

If your first pseudo code example is the way that ROAM priority queues work, it does seem like a bit of overkill. Though if you had a totally frame coherent algorithm, with coherent priority queues (and perhaps the trees themselves essentially stored in the priority queues), I can see how it could work.

Glad you like the game.