Way back when, I ran dhrystone tests on both eCos and Linux on the same MBX board. The version on Linux ran quite a bit faster. Possibly missing some board initialization magic in the HAL.
I just noticed that the performance of the MBX board when running from RAM is less than 50% of what it is when run from ROM. This is most likely a RAM vs. ROM hardware configuration problem (the RAM is DRAM which runs via a complicated setup). Fix this anomaly and you'll probably fix the Dhrystone performance problem as well.
The caches were not being set up properly, certainly not for RAM based applications. This has been fixed and the Dhrystone benchmark now runs more than 4 times faster than before.