This is an unknown area for the xw series of workstations...... I'm probably going to do the experiment based on the device discussed in detail in a currently active thread in the forum, based on the fact that Brian has proven it works in his Z600. Take a look HERE.
An important thing to know is that there are two main types of M.2 SSDs.... M.2 AHCI SSD and the M.2 NVMe SSD. I'm quite sure the HP Turbo Drive is a NVMe type, and there is a special BIOS upgrade for the Z620 etc. that is necessary for it to work on it, plus the more advanced hardware built in to the motherboard. There is no such BIOS upgrade for any of the xw workstations, and the technology of those older motherboards likely could never accept a NVMe type of SSD. The AHCI type of SSD, however, has a strong chance of working for the xw workstations, and that is the type that Brian has up and running on his Z600.
There is a partial listing of the two types of M.2 SSDs on the web page of a high end M.2-to-PCIe adapter that has been discussed recently in this forum. None of these HP workstations have the M.2 slot built into its motherboard so you must use an adapter. You can see one HERE, and focus only on the AHCI type of the M.2 SSDs. Note that Brian's is not on the list, but that is because not all have been tested by that company. I think that product is likely A+ quality but over the top for what most of us would be doing with an xw generation workstation.
The xw series of workstations all are SATA generation II, as are all of the ZX00 workstations (such as the Z600). If you are thinking of using a M.2 AHCI type PCIe SSD adapter as an upgrade from a hard disk drive in your xw4600 I think you should instead simply buy a used Intel 320 series 160GB SSD (or, better, a 300GB version). That will certainly work fine.... we are using lots of those, and you'll get performance well balanced with that workstation's capabilities.
You have significant room for improvement by installing a faster processor and making sure you have identical faster RAM sticks (you probably have the slower of the two types now) fully populated in your 4 memory slots. Find the very latest QuickSpecs for that workstation that you can to see the fastest processors it is certified for, and make sure you get the latest sSpec code for that when you buy it used off eBay. Make sure to upgrade your BIOS to the latest first. After that then you might be able to justify a M.2 AHCI type SSD adapter that you can boot from and run your programs from. Your basics are not optimized yet, actually.
The latest QuickSpec I just found for the xw4600 was version 22 and the fastest Quad Core listed then was the Intel Core 2 Extreme QX9770 Processor / 3.2 GHz, 12 MB L2 cache, 1600 MHz FSB. There is a single sSpec for that on the Intel Ark site of SLAWM, but that looks too expensive to justify buying off eBay. So, just step back one step and take a look at the second fastest, the Intel Core 2 Quad Q9650 Processor / 3.00 GHz, 12 MB L2 cache, 1333 MHz FSB. That also has only 1 sSpec code (SLB8W) and on eBay that can be bought at a reasonable price for that workstation. You can run those under the Mainstream rather than the Performance heatsink/fan for the xw4600.... we have a good number of the 95W max TDP processors in our xw4600s I upgraded that way, running for quite a few years now. Your Q9660, however, was a hot processor at 105W max TDP so you likely have the Performance fan already.
Yep, got the xw4600 booting up and running with a M.2 PCIe drive in an adapter plugged into a fast PCIe slot. It is a M.2 Kingston drive, the Predator, and it has an AHCI controller chipset built into the M.2 card itself so it can use the legacy BIOS that the xw and the ZX00 generation of HP workstations run on.
So far I have not been able to get a Samsung SM951 (AHCI version) to work with a similar adapter. So, Kingston has some magic sauce. I also have gotten that Kingston card running as my boot drive in the xw6400, xw6600, Z400, Z600 and Z800.
To use its speed best it should be placed in a PCIe slot that is at least PCIe generation 2 and at least 4 "lanes" wide. For the xw4600 I used the lower of the two PCIe x16 "video" slots. Works fine in that.
I have posted in here on how it would work with the Z600 with only one of the two storage controller driver sets that HP has currently available on their Z600 drivers site..... you can search for all those Predator posts here using the top left forum search box.