^ Not true
Concur with WyomingKnott, I do not recommend raid0 SSDs used as a Boot + program drive. You chouice if used as a Data drive.
To answer your question on speed. For sequencial read/writes. Over all will depend on (a) strip size and (B) the size of files being called. For example using a 64 K strip. If the file size is less than 64 K then all of the file will be on one drive and the speed will be dictated by that drive. If the file is split (<64 K) then the speed will be dependent on both drives, part of the file would be at drive 1 speed and part of the drive would be at drive 2 speed and will be somewares between the sum of the two but less than 2 x the fastes drive.
.. Improves Sequencial performans, the LEAST important matrix for an OS + Program drive. Important for a data drive when working with LARGE file structures.
.. Does NOT improve access time
.. Very litel improvement for the more important 4 K random read/writes.
Improves sequencial speeds