gdi+ Graphics::DrawImage really slow~~

If you're using GDI+, the TextureBrush class is what you need for rendering images fast. I've written a couple of 2d games with it, getting around 30 FPS or so.

I've never written .NET code in C++, so here's a C#-ish example:

Bitmap bmp = new Bitmap(...)
TextureBrush myBrush = new TextureBrush(bmp)

private void Paint(object sender, PaintEventArgs e):
{
    //Don't draw the bitmap directly. 
    //Only draw TextureBrush inside the Paint event.
    e.Graphics.FillRectangle(myBrush, ...)
}

You have a screen of 4000 x 3000 resolution? Wow!

If not, you should draw only the visible part of the image, it would be much faster...

[EDIT after first comment] My remark is indeed a bit stupid, I suppose DrawImage will mask/skip unneeded pixels.

After your edit (showing StretchDIBits), I guess a possible source of speed difference might come from the fact that StretchDIBits is hardware accelerated ("If the driver cannot support the JPEG or PNG file image" is a hint...) while DrawImage might be (I have no proof for that!) coded in C, relying on CPU power instead of GPU's one...

If I recall correctly, DIB images are fast (despite being "device independent"). See High Speed Win32 Animation: "use CreateDIBSection to do high speed animation". OK, it applies to DIB vs. GDI, in old Windows version (1996!) but I think it is still true.

[EDIT] Maybe Bitmap::GetHBITMAP function might help you to use StretchDIBits (not tested...).

Just a thought; instead of retrieving the width and height of the image before drawing, why not cache these values when you load the image?