The person in that 'edugeek' post is me!
The particular RAID in question is still running one side with 5x 256GB SSD in RAID 5, and 5x 500GB SATA 2.5" traditional drives in RAID 5 on the other. Over the past year there have been no faults or stability problems running an XServe RAID "hacked" in this way.
There is not a dramatic performance improvement in all honesty. I don't have any benchmarks to hand but I would say there is a slight improvment in performance. Things to remember are, particularly for our set-up, that there is only 2Gbps in to this XServe RAID over fibre channel, and we use ours for network home folders so it handles requests for everything typically 70 concurrent users may need, per side - more or less depending on which combinations of year groups are on the system.
I do love the XServe RAID and have had 4 since they were introduced, to when they were discontinued, through various hacks and enhancements to keep them in business to today. We've kept them running with refurbished parts but it is now sensible for us to look at replacing them - staring in a couple of months. There are current, supported, products out there with faster I/O to the host, and faster I/O to the drives, as well as using standard readily available HDDs rather than IDE drives in a specialist carrier.
That said, I don't know what your application is!