Wireguard maxing out at 120Mbs

[xternal`]

Hi all
I have just upgraded to a fibre connection which is 1Gbit. If i connect directly with my laptop and Mullvad wireguard i get speeds about 5% slower than than the native connection.
On my my APU4 PCEngine with opnsense I get max 120Mbps.
I have tried changing MTU and simplifying the routing tables. No changes and unlikely to be the issue as my fibre connection doesnt use PPPoE.

Any ideas how I can get my opnsense box to achieve the same speeds? It is the latest version with the kmod as default. The cpu is also not even 10/15% when doing the speed test

[xternal`]

On further inspection, it appears there is a CPU bottleneck on CPU0 when wireguard is enabled.
When wireguard is disabled, the is obviously less CPU overhead across all 4 cores
When it is enabled, CPU0 does all the interupt heavy lifting and the other cores whilst have system usage, interrupt usage in top is minimal.

Not sure how I fix that though, I have tried lots of different tunables from the forum but nothing seems to make a difference