Mmm, depending on other factors also, Neil, increasing piston weight or opening the TP might cause it to produce even more power.. Unless the TP is already at its upper size limit, in which case creating that bit more lost volume might help drop the power.
I'd be tempted to source a different, softer spring, or to shorten the existing one a little (although the latter approach will make the spring stiffer). Either way will also result in easier cocking. If you already have minimal preload, I'd definitely go longer / softer spring, as too little preload will likely result in increased piston bounce.