How to enlarge qemu display ?

[Pierre Couderc]

I use a XP guest  in qemu on  linux.

I use a 4K monitor and my 800x600 XP windows is very very small, lost in 
the 4K monitor.

I do not want  to change my 800x600 size nor my monitor.

But I would like to enlarge the XP window so that a XP pixel be mapped 
on 4 monitor pixels, or even if possible on 2 or 2.5 or 3 pixels.

Is it possible...?

Thanks for any help !

PC