Yes, 25 mg is a low dose, and if you can get away with taking it before bedtime it should have (ER or not) minimum side effects during the day. On the other hand, you my need the strength during the day...morning dose may be necessary, follow you doctor's recommendation and/or your experience.
I think the low dose Metoprolol is about as minimum impact you can take and hope it will still help.
Higher dose of Metoprolol will most likely interfere with your physical activity, as it will surely lower you blood pressure, and maybe too much. I've taken as much as 200 mg a day (100 morning, 100 night) and it really puts me down. I'm now on 100 mg (50 by 50) and tolerate that well.
I'm about 6'6" and 240, so our size is similar, not sure size matters in terms of the side effects.
Good luck, let us know how it works out. We are a collection of experiences here, not medical professionals. So we learn and share experience in the hope it helps others figure out what is going on.
I was going to suggest metoprolol since that is acutally used by some athletes to lower heart rate so they can go longer.. I only take 12.5mg XL to control occasional SVT