To my knowledge there is only an one-sized magnet - the TD-124 and TD-135 alike.
Never read anything about two different sizes. The TD-135 has only a smaller bearing than a TD-124. For the rest, the motor etc are alike.
See also http://www.theanalogdept.com/eddybrake.htm
Why do you need a more powerful brake. You don't have to make an emergency brack. It just needs to easily slower down the platter. No full stop in 1 sec.
Furthermore, my TD-135 is working fine on 230 volts so I don't see or heard of any problems when switched from 220 to 230.
Just try and enjoy!