Well unless you are using modded RST OROM/drivers, Intel's official RST drivers don't support trim in RAID0 on the z68 chipset (at least last time I checked). If you are thrashing your drives with benchmarks, this could cause speed issue "feelings" as the free blocks get used up quickly.
Try going to a single SSD see how the drive feels/performs since trim definitely works on single drive SSD's with Intel's official OROM/drivers on the z68 chipset. You will suffer slower "big" sequential type benchmark numbers though (aka ATTO), but benchmarks aren't generally reflective of real world normal usage. For example, you can have a particular drive that does awesome in IOMeter with giant queue depths, but since normal desktop use rarely exceeds 1-4 queue depths, the drive might not perform any better in normal desktop usage (I.E. server tuned SSD's vs desktop use).
Trim support is generally better/more important for normal felt performance than a small RAID without trim support, especially on smaller drives that have a higher percentage of used space compared to larger sized drives. You can get away with more using larger drives without trim, simply because you have a lot more blocks for the controller to work with, but thrashing any SSD RAID setup with constant benchmarks without trim support is not optimal in any case, especially if it's also the boot/OS drive.
In my experience, RAID0 with SSD's is good for benchmarks, but offers little actual "performance" benefit in normal usage over a single decent SSD, especially if it's the boot drive. Now if it's reserved for use (aka, non-boot drive) for a particular reason like a particular application's scratch drive, it can be awesome, but as a boot/OS drive, RAID0, especially without trim support, is more a pain than it's worth.