Confused about SAS Raid/HBA speeds

[essential+]

Got 2 questions about SAS raid controller cards and HBAs.

 

First question
 

If I had 256 SSD drives (using SAS expanders of course) in raid 0 connected to a 6Gb/s SAS raid controller (PCIe 2.0), what theoretical speed would I get:

1. 256 x 6GB/s ?
2. 6GB/s ?
3. The maximum speed of the PCIe 2.0 port?

 

Second question

 

Does the reply to the first question also apply to HBAs, provided a software raid is used instead?

[Xahid]

I have 256 GB SSD connected with SAS raid controller 6Gb/s from IBM.

6Gb/s speed is written on the SSD, but I don't think it's the actual speed of drive (practically) I am using it only for OS, and other SAS drives 500X4 GB Raid5 for Database.

I think you will get full SSD speed even if its connected to SAS controller, it will not dramatically speed up the SSD.