bokeh – Prime lens is over-exposed fully open, when in full daylight

I bought a Lumix f/1.7 25mm prime (H-H025), to use with my OM-D E10.3

When fully open on a bright sunny day, with the ISO set to 200 my shutter speed flashes at 4000 to indicate it’s out of range. If I drop the EV down to -1 the images are still washed out/overexposed.

Other than going back a few stops until I get an acceptable shutter speed, what else can I do to ensure a good level of exposure, and a sweet sweet bokeh?

Should I be going all the way down to -5 EV? And if I do, what (if any) side-effects will that have on image quality/sharpness on the focal point?