While playing a simple file with Winamp 5.01, I found a very big difference between VBR and CBR CPU usage:

VBR --alt-preset standard: 15-25%
CBR 192kpbs : 1-2%

I used lame 3.93.1 to encode the files.

I agree that VBR need more resources than CBR, but that's a big difference.
Is it normal?
Did I do something wrong?

Using Winamp "Classic" 2.81, I noticed no difference betwixt CBR & VBR.

BTW, you most probably should be using HA's recommended build of LAME; 3.90.3.
Get it there.

I tried with lame 3.90 but it didn't resolve the problem.

But I did the same test with WMP Classic and the CPU usage was quite the same between CBR and VBR.

Conclusion: It's a Winamp 5.01 problem. I think I will try to reinstall my old MAD plugin.

On my system VBR and CBR files play in Winamp 5.01 with 0-2% CPU usage. I also use LAME 3.90.3.

I found the problem!!!
It was really stupid.

I just configured the in_mp3 plugin to display average bit rate and not real time bit rate. And everything became OK.
Real time bit rate happens to need A LOT OF resources.