In general, it can be easier to volley a hard flat shot than a slower one. Before you start trying to blast the ball 100 mph, see if taking off some pace or slicing will trip him up.
This is level-dependent, I must admit. At my level (4.0 ladies), there are many players who don't have the most solid volley mechanics and will struggle to generate their own pace/penetration on a volley.
-- Random Error Generator, Version 4.0
-- Master Moonballer