In darker conditions, you could either increase the aperture or increase the shutter speed. Both would work well. The difference between the two is the creative effects. If your shutter speed is too long, then your image might appear blurry from the shakiness of your hands. This could be mitigated by using a tripod. For the 44mm lens on your Bolsey, any shutter speed equal to or faster than 1/50th will prevent camera shake. Your aperture impacts your depth of field. Wider apertures result in less depth of field, meaning your zone focusing would have to be more accurate too. Smaller apertures result in more depth of field, meaning you have more wiggle room with your zone focusing. Very wide and very tiny apertures also decrease the sharpness of your image, but that shouldn't be a big issue on the Bolsey B2. Photography is a game of trade-offs; a tiny aperture might be ideal, but your image might be really shaky because you had to compensate for that small aperture with a long shutter speed. A short shutter speed might be ideal, but your image might be our of focus because you had to compensate with a wide aperture and small depth of field. Instead of considering only aperture or shutter speed, you should try to balance the trade-offs.
It seems to me like f5.6 and 1/200th at iso 200 is probably good enough for overcast. It's impossible to know without a light meter, but color negative film has a wide exposure latitude so slight under/over exposure shouldn't be an issue. I don't know if expired film holds its exposure latitude, but hey, that'll be interesting to figure out when you get your shots developed.
There are machines designed to test shutter speeds. I don't have one, so I try to measure shutter speed by ear. If you have a digital camera that you know is accurate, you can listen to different shutter speeds and compare them to your Bolsey. You could also do this by eye, but I find that my hearing is better than my vision.
If you're mechanically inclined, then maybe you could try repairing the Bolsey's slow speeds. I really like old manual cameras because they're simple to repair.