I tested the same NVMe in two generations of PCIe slot and learned why most people are upgrading wrong

At a glance:

• Upgrading from PCIe 3.0 to 4.0 SSDs delivers only marginal real-world performance gains for typical users.
• The Seagate FireCuda X1070 SSD showed 50% slower speeds in PCIe 3.0 mode (3,534 MB/s read) versus PCIe 4.0 mode (6,918 MB/s read), with no perceptible difference in daily PC responsiveness.
• PCIe 4.0 SSDs primarily benefit creative professionals handling large files, while most users can postpone upgrades until storage capacity is exhausted.

Background: Why This Test Matters

I've written extensively about why you don't really need a PCIe 5.0 SSD, but what about earlier generations? If you have a PCIe 3.0 SSD and upgrade your motherboard, do you need to change the SSD as well? What about if you see an excellent deal on a PCIe 4.0 SSD? Is it still worth it if you're on a motherboard with Gen 3 slots? I wanted to do a little testing because my gut feeling, after building so many PCs over the last decade, was that it doesn't matter as much as you think. I've been an early adopter of every new storage medium, and the biggest jumps I felt came from hard drives to SATA SSDs, and then from SATA SSDs to NVMe (of any generation).

Understanding PCIe Generations

Each PCIe generation doubles the effective bandwidth. PCIe 3.0 provides 32 GB/s of bandwidth with a full 32 lanes. NVMe SSDs use x4 lanes from the motherboard, so this gives a max bandwidth of 4 GB/s. PCIe 4.0 increases this to a maximum of 8 GB/s, meaning that with protocol overhead and other factors, most Gen4 SSDs top out at around 7,250 MB/s read speeds. The following table details the specifications across PCIe generations:

But do you actually need all that speed? Let's put it to the test and talk about the real-world implications.

The Test Subject: Seagate FireCuda X1070

The Seagate FireCuda X1070 is the company's newest gaming-focused PCIe 4.0 SSD. It's pretty indicative of a mature Gen 4 drive, with 7,200 MB/s max read and 6,500 MB/s max write speeds. The 2TB capacity we're testing draws 4.7W of power on average and uses the full x4 PCIe Gen4 lanes from any M.2 slot. It's also DRAM-less, which is probably okay for the PC gaming handhelds that it's positioned for use with. Note that it'll only work in devices like the ROG Ally X that support a 2280 SSD; it's too long for the Steam Deck, Legion Go 2, and others.

Benchmark Results: CrystalDiskMark and ATTO

Looking at CrystalDiskMark, in Gen 4 mode, the SSD has a read speed of 6,918.60 MB/s and a write speed of 5,064.54 MB/s. That's a little under the manufacturer's specifications, but still in Gen 4 territory. When restricting the PCIe slot to Gen 3, that drops to 3,534 MB/s read and 3,521 MB/s write. That's as expected; dropping down a PCIe generation without losing any lanes should cut the effective bandwidth in half, and speeds will drop as a result. What it didn't do is make my PC any slower to use while navigating through Windows.

Atto shows the same pattern of the speeds dropping in half as we go down a PCIe generation, but at no point did my PC feel 'slow.' The only real reason I upgraded from PCIe 3.0 NVMe drives is that the ones I had were only 256GB, since they were expensive compared to hard drive capacity at the time.

Real-World Performance Implications

Transfer speeds aside, will those actually help you in daily use? Windows or Linux won't boot any faster on a Gen 4 drive compared to a Gen 3 drive. That's down to firmware and BIOS initialization, driver initialization, and small-file access. Don't believe me? My Steam Deck is PCIe 3.0 all the way through, and it boots just as fast as SteamOS or Bazzite installed on a ROG Ally X, which has a Gen 4 SSD. Gen 4 drives are often more power-efficient and have higher endurance figures than Gen 3 drives, but that doesn't matter much on a desktop platform, and I haven't worn out an SSD yet through normal usage.

The one place where the increased bandwidth comes in handy is when working with large files in video editing or similar creative workflows. It's still not a huge difference, but every second counts when you're a creative professional, and in that case, Gen4 makes more sense.

Upgrade Advice: Do You Really Need a Gen 4 SSD?

PCIe is backward-compatible, which means even a Gen 5 M.2 slot can use Gen 3 drives, and vice versa. But like, upgrading to a PCIe 5.0 SSD isn't necessarily worth it if you're just upgrading your motherboard. It's a trap that I've fallen into with every platform upgrade, and really, the only reason you need to upgrade for everyday tasks is if you're running out of storage space. The jump from SATA to PCIe NVMe was a much more meaningful improvement on daily responsiveness, and honestly, even SATA SSDs are fine for daily use. Several of my systems still have SATA SSDs, although I've moved all my hard drives into storage servers to keep the noise level down. And really, at a time when NAND pricing is out of control, any good news about being able to put off storage upgrades until later is welcome.