HD Tach was run in compatibility mode (otherwise it wouldn't start), windows seven 64 bits. Regarding IO Meter, from my understating it uses the free available space to test the SSD, so it writes a new file and then uses it to test the performance, which is not my issue as new files are fast. (the 100% read performance is above 500 MB/s, with the settings you recommended)
Now I did the test with HD Tune which shows the same tendency as HD Tach:
