Amp Power: Tubes vs Solid State

That all depends what you mean by a difficult load. If it's a higher than typical impedance load many tube amps may have advantage. If it's a lower than typical impedance load many solid state amps will have an advantage. Many lower powered tube amps will clip more gracefully than a solid state amps. Many solid state amps offer more power per dollar. IMHO it's a moot point. First find the appropriate tools for the job, the decide which tool you prefer to work with.

Technically speaking a Watt is a unit of measure of power, as such a Watt is a Watt. The fact that tubes clip more gracefully is similar to a stone rolling (tube Watts) down a hill (point of overload and subsequent distortion) as oppossed to a stone falling (solid state Watts) off a cliff (point of overload and subsequent distortion). Of course you can avoid frequenting the point of overload with more Watts.