Opinions: PC's with strong lows roll off the highs

In the past months I've been trying quite a few different power cords in my setup. A fellow Agoner that is very knowledgeable about power cords stated that power cords that support strong low end performance generally roll off the highs. More and more, that experience seems consistent with me too. I'd sure like to find a reasonably priced cord (closer to $500) that can support powerful low end performance and maintain extended highs. Do you have an opinion on this based on your experiences? We know this is all system dependent, but have you found a power cord that can perform both frequency extremes with no roll off?