Look 25Gbps is crazy fast internet. This starts to get into the category where you need dedicated router ASICs etc. General purpose computers should be ok up to about 10Gbps. But think about it this way, at 10Gbps you can process 10e9/1500/8 = 833k packets per second. At 1Ghz that's about 1200 clock cycles per packet. Which is around 1 clock cycle per byte.
I have never heard about 25Gbps before so how can anyone have tried it since 10Gbps is extreme level.
I am not really sure how many cores Openwrt actually can use, if it actually can use 8cores that actually do anything simultaneously.
But that processor run at max 5GHz per core, hopefully the drivers handle data on both pos and neg flank so that means 10G thoughts per second per core, which is where your 9,5Gbps you mention end up, plus overhead to manage the router internals.
If you want to think about the content of 25Gbps data in the router you need more power. A lot more power.
25x faster is like going from 40 Mb to 1Gb all over again. It would of course be interesting to try and compare since they are completely different kernels and drivers. But at the end both OpenWrt and Opnsense are both built around the networking stack of a general-purpose OS running on a general-purpose CPU.
You seem to have the appropriate WAN network and corresponding hardware (at least SSD and RAM are a bit of a waste, but that's not a problem either), now there's just one thing left to do - test OpenWrt.
Just write it to a USB stick and have a go, shouldn't take you more than 5 minutes (if the necessary NIC kernel modules are packaged, if not, you'd have to do that first and build from source, not trivial, but very much doable, especially for x86_64). Admittedly, >=10 GBit/s might warrant some further fine tuning for optimal performance, but you should already get a good first impression in next to no time.
You'll know after testing it (size or performance of the block storage, aka SSD vs USB stick, does not matter in the slightest for OpenWrt and its ability to route at full speed). Practical experiences above 1 GBit/s are already scarce, 10 GBit/s even more so - I have not heard of anyone trying beyond that so far - so be the first to find out.
One way to get a (very?) rough benchmark for a specific OS's throughput is to run iperf3 tests between two sessions on the same machine, using the loopback interface. Since this takes the NICs right out of the equation, you get a feel for how the software behaves.
Here's what I see running OpenWrt 22.03.2 on a 4-core AMD Jaguar (apu2):