Well, Silverflames are good heads and really sharp. Being as both heads are the same brand and equally sharp, I'd probably go with the narrow, heavy one as the narrower head will have a slight edge in penetration.
However, since there is a weight difference, you may have flight issues due to different spine requirements. If the wider (lighter) head flew better due to it being better matched in weight to your arrows and bow, I'd shoot it instead.
If both shot equally well, I'd be back to choosing the narrower head for that little extra penetration edge.