One of the things with SSD'S is that when you look at the spec's they always seem to say " up to " when listing the speed of the SSD. Just one of those things you don't seem to notice when reading the spec's. Where did you buy this SSD from ? If you just bought it and can return it , do so and get another there is always the possability you have a defective one.
Yes, the Intel Sata III and using the Intel latest RST version 10.6 provide better performance than using the marvel basaed Sata III port and mavel's ahci driver.
How much of a hit, Not sure. OCZ sata III drives that use the SF2281 controller. This provides very high Sequencial read/writes when uncompressed data is used in the bench mark. 2 things, (A) Sequencial read / writes are the least important function, the Random 4 K read/writes are what are important for a OS + Program drive. (B) Real life data is not nearly as compressable.
Your SSD is performing exactly as advertised.
"UP TO xxxMB/sec"
The ATTO benchmarks by default measure sequential I/O using overlapped I/O and a queue depth of 4.
I doubt that you have any app on your pc written that way.
Fast random I/O of small blocks at low queue lengths is what the OS does mostly, and any SSD will do that exceedingly well. Response times of 0.1ms would be typical, and that is 100x faster than a conventional HDD.