Thank you! 
I’ll give it a go…
For now:
Stock driver:
Block Size 4k Write 0.556641 Rewrite 0.798828 Read 3.95605 Reread 3.94141 Random Read 3.84375 Random Write 0.529297
Block Size 512k Write 13.3008 Rewrite 10.1299 Read 18.3818 Reread 18.3545 Random Read 18.0508 Random Write 4.22168
sdhost driver:
Block Size 4k Write 0.577148 Rewrite 0.837891 Read 3.99121 Reread 3.99023 Random Read 3.80078 Random Write 0.527344
Block Size 512k Write 19.3174 Rewrite 14.8604 Read 22.0576 Reread 22.0605 Random Read 22.0059 Random Write 11.5205
mSDcard is a Sony 16GB SR-160X (not more info that I can gather from it…)
…and it’s stable as far as I could test it…