How to get the progress of a TRichEdit?

I have a simple 'brut' big text file (20MB). I would like to show it in a TRichEdit. The problem is that it takes 6 seconds for the showing. I would like to put a progess bar in the bottom of the application to avoid this bad UX design.

My question is how to get the progress of the TRichEdit showing ? With the TRichEdit::LoadFromStream method, it goes from 0 to 100% fast (less than 1 second) but after the application wait 6 secondes during the first show.

I created this class FileStreamProgress with TFileStream inherit. I overide the TFileStream::Read()

    int __fastcall FileStreamProgress::Read(void *Buffer, int Count)
    {
        __int64 previousPosition = this->Position;
        int ret = TFileStream::Read(Buffer, Count);
        if (this->Position == 0 || this->Position == this->Size || (previousPosition/128000) != (this->Position/128000)) {
            ProgressCallBack(ProgressCallBackParam1, this->Position, this->Size);
        }
        return ret;
    }
    static void FileStreamProgress::ProgressCallBack(void*thiz, int i, int max)
    {
        TProgressBar* ProgressBar = (TProgressBar*)thiz;
        if (ProgressBar)
        {
            if (max > 0)
            {
                ProgressBar->Position = int(i * 100 / max);
            }

            if (Application)
            {
                Sleep(1);
                Application->ProcessMessages();
            }
        }
    }        

This is how I test it :

void MyApp::CreatePage(AnsiString filename)
{
    ProgressBar->Visible = true;
    FileStreamProgress::ProgressCallBackParam1 = (void*)this->ProgressBar;
    TFileStream * stream = new FileStreamProgress(filename.c_str(), fmOpenRead);
    TPageMemo* Page = new TPageMemo(this);

    Page->Parent = PControl;
    Page->PageControl = PControl;

    MessageDlg("111",mtError,TMsgDlgButtons()<<mbOK,0);
    Page->Texte->Lines->LoadFromStream(stream);
    MessageDlg("222",mtError,TMsgDlgButtons()<<mbOK,0);

    PControl->ActivePage = Page;
}

There are 7 secondes between the 2 message dialogs "111" and "222". And my progress bar wait 6 secondes at 100% (during the showing)

I tried to go deeper with the win32 API's SendMessage and Handle without the expected result.

At the end, I used a TMemo yesterday cuz it's a brut text. It's very fast (instant open) but some functions are missing like FindTextW(). I rewrote it. Thanks

http://docwiki.embarcadero.com/RADStudio/Rio/en/Memo_and_Rich_Edit_Controls