To clarify, speakers do not “have” wattage. They have a power-handling capacity. It means little in terms of tone unless you need to overdrive the speaker slightly for that saturated sound but be careful; if you drive the speaker hard enough, it could fail. As the EH guy said, you won’t blow the 80 watt capacity cabinet’s drivers. Any speaker rated 35 watts or more would be hard to blow. You could use a 25 watt rated Greenback; just be cautious.