The difference between 100 watts per channel and 200 watts per channel is 3 dB, or "somewhat noticeable" difference in loudness. It's not really significant unless you're driving inefficent speakers. You can approach the maximum wattage during very dynamic movie passages, depending on how the receiver power ratings are published.
For example, a Rotel receiver will be advertised with a rating of 100 watts x 5, all channels driven, 20 Hz-20 kHz. A Panasonic receiver will be rated as simply "100 watts x 5", which usually only means 100 watts is available to any given channel at any given time...the all-channels driven output will be something like 35 watts, which can cause clipping if you set the volume too loud. I had an el cheapo Technics receiver once upon a time which constantly went into protection mode, despite being advertised as "90 watts x 5".
I'm not sure about KLH, but Sony is notorious for overstating power on their receivers. Spending the extra bucks on a receiver with a more stable power supply (Denon, Onkyo, Yamaha) is well worth the investment.
