Delphi default MM is a cut-down version of FastMM4 on Windows.
You may achieve slightly better performance on multi-threading by using FastMM4 with some custom conditionals.
IIRC on Apple, Linux or mobile platforms, it uses the clib heap manager. Which is not bad in practice.
ScaleMM2 or others - like BrainMM - may be better for multi-threaded apps, but tend to consume much more memory.
Under Linux, switching to Intel TBB or JMalloc may give a performance boost, but will also consume much more memory - see my tests with FPC https://github.com/synopse/mORMot/blob/8a55fb3bf2d4cffeb779dd19a8be18e227188f2f/SynFPCCMemAligned.pas#L68
But the main performance enhancement would probably be by changing your algorithms...
Mainly avoiding heap allocations...
See http://blog.synopse.info/post/2018/11/12/EKON-22-Slides-and-Code