any luck renanbirck?
I'm just going to share my experience.
I've tried many combinations of gcc flags, including the vendor specific memory flags you mention, but no luck ...
msp430-gcc blows the roof compared to the legacy mspgcc.
Here is are some numbers (bin.legacy is mspgcc, bin is TI msp430-gcc 3_03_04_00) for a given application:
$ msp430-elf-size bin/wizzimote/gateway.elf bin.legacy/wizzimote/gateway.elf
text data bss dec hex filename
29532 1564 1054 32150 7d96 bin/wizzimote/gateway.elf
10120 12 1846 11978 2eca bin.legacy/wizzimo