Clipboard size limit
Applications call GlobalAlloc(GMEM_MOVEABLE or GMEM_DDESHARE) to allocate the memory for data to be stored on the clipboard and make it available to other applications. For 32-bit applications GlobalAlloc can allocate blocks up to 2 GB in size or up to the amount of virtual memory the PC has, whichever is less. The Windows clipboard does not impose any other size limits.
Most data is copied as a reference rather than the data itself so you can copy most anything any size. Text though is actually copied and from what I know the amount of data is limited to how much ram is currently availiable. Remember this, if vb6 can handle it, I'm sure the clipboard can handle it.