Thanks. From your reply:

In terms of rendering performance this will be the most performant implementation, but might be a problem, when you need to implement operations on individual element ( f.e drag&drop or controlling an specific stacking order ).
"most performant implementation" - is it best performance implementation?

Ya, I will be trying these three options and see the performance in simulation. There will not be any graphical operations on the plot items; simply plot and move them on the display according to their instantaneous position. At most, tracker text/ context menu will be provided for mouse hover/ mouse right click on an item.
Actually, also, a unique number is to be displayed along with symbol; that is why I was thinking of customizing a plot item by deriving from QwtPlotItem.
So, I assume, the steps for movement of plot items on plot area would be: i. Create item. ii. Attach item to plot. iii. Detach/Delete and Attach it again at new position.

Thanks for your suggestions.