You may want to check your math...... 500MB/s = 500 megaBytes per second.... Thats a gig of data every 2 seconds! I think your getting confused with 500MB/s and 500Mb/s. 500Mb/s (note the lower case b) is 500 megabits per second (not bytes). There are 8 bits in a single byte of data.
So if the card is 500MB/s which it is, then that really means 500 megabytes of data a second. If the card is 500Mb/s (which it is not) then that means 500Mb/8= 62.5 megabytes per second. Also the chipset in the card does not distibute and limit the the data per port. 20 drive connectivity does not mean that each individual port is limited to 25 MB/s. It will theoretically push 500 megs in/out a single port, the drive it's self is the limitation. But if you did have a 20 drive raid 0 array running it will only pull 25MB/s per drive..... but that total will still equal 500MB/s! 10 drives still 500MB/s (50MB/s per drive)....etc....
And the 333MHz chip is till ample power all that is doing is dedicated file addressing. A solar powered calculator is fast enough for that.
By the way, I do not own one of these cards but I do own a G-Technology eS Pro 8 drive array (2x4) which includes a mini-SAS card (831MB/sec Raid 0, for editing RED camera 2K resolution video, but could handle 4K), yes that almost a gigabyte /second!
Im just trying to pass along some info..... don't hate me!