This shows that the "new" version encodes a bit slower (but certainly
not two times!) in VBR mode and encodes quite a bit faster in CBR mode, compared to the "old" version.
I can't see how this matches your previous report
How exactly did you measure the speed of LameXP v4.03 against v3.18 on your system before? And are you absolutely sure that you got the latest build of LameXP v4.03 (build #664 at this moment) ???
Also: Is your processor single or dual core? And how many encoder instances are you running in parallel? How is the CPU usage - encoder process(es) -vs- LameXP main process - while encoding?