I wouldn't bother with nvme until you can upgrade the motherboard for native support. IO sequential reads are quick enough on sata 3 6gbs ssds which you have 4 sata slots for, 2 on main z68 chipset and 2 by Marvell.
It is possible to get nvme running on your board with that adapter but there are some things to be aware of.
1. Booting not possible unless bios is modified to include the modules.
2. All pcie slots are gen 2. So if you used the small pcie slot that is 1x then the transfer rate will be around the speed of a normal sata3 drive ~500MBs. This 1x slot at the top may be awkward getting to if have a gpu next to it or could move gpu to the 2nd 16x slot.
3. It may be possible to use one of the 8x longer slots for an 4x nvme adapter (only for storage without modding bios) which at pcie gen 2 speeds at 4x may see around 1500MB/s ~ give or take.
https://forums.evga.com/m/tm.aspx?m=2531123&p=1#targetText=PCIE 2.0 X4 has 2000,high performance PCIE NVME SSD?
Im not 100% on facts here, it's just what I've gathered looking around trying to find out if it's worth you going nvme instead of sata. Imho, if just gaming and not needing extreme transfer rates for data transfer then go sata.