To be safe, would you not just set the best glide speed by using full back trim, as every SEL that I know will have the best glide speed by using full back trim?
Well let's confirm the malfunction.
If you think you have picked up some carb icing, or have a solveable fuel delivery problem, then you will want to stay in the air as long as possible while you sort it out. The best speed will be minimum sink speed, which is slightly slower than best L/D, and not affected by wind.
If you have a con-rod sticking out of the cowl and a landing is inevitable, you might want to glide as far as possible. With a headwind, speed for best glide is faster than best L/D, which I think is what Darkroom is calling "best glide speed".
And please, nobody mention the once-taught technique of turning downwind to cover more ground!