Take a look at this recent pic from my last outing in a pretty strong wind. (We were advised at the lodge that "we may not wish to proceed".

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The waves were manageable to about halfway down the wind, with drift re-set from there. With a fresh battery the engine just coped despite the prop being lifted out cresting some bigger waves.
It's probably not much compared to the big Lochs/Loughs but I've posted the pic for an idea of wave size rather than just wind speed - I'm new to drifting a boat but wouldn't fancy drifting in much more of a wave than this as it was my back kept getting washed over.
Further, to give an idea of conditions in this size of wave, an experienced forum hand also took a boat same day. His battery/engine packed up and he got blown on to the downwind shore, considered ditching then called it a day by lunchtime (probably the more sensible out of the 2 boats).
If you are in a wheely boat I would not have attempted in those conditions.