PC got slower over the years. CPU vulnerability mitigations?

Hi,
I'm using a PC running debian stable for signal processing. A few years ago it was just fast enough to do the job, but over the years it got slower and now it isn't fast enough anymore for the same task. It's CPU limited.

I think it might be due to CPU vulnerability mitigations.
It's a Haswell (i5-4690K), which isn't affected by retbleed, but others:

Code:# grep . /sys/devices/system/cpu/vulnerabilities/*
/sys/devices/system/cpu/vulnerabilities/gather_data_sampling:Not affected
/sys/devices/system/cpu/vulnerabilities/itlb_multihit:KVM: Mitigation: VMX unsupported
/sys/devices/system/cpu/vulnerabilities/l1tf:Mitigation: PTE Inversion
/sys/devices/system/cpu/vulnerabilities/mds:Mitigation: Clear CPU buffers; SMT disabled
/sys/devices/system/cpu/vulnerabilities/meltdown:Mitigation: PTI
/sys/devices/system/cpu/vulnerabilities/mmio_stale_data:Unknown: No mitigations
/sys/devices/system/cpu/vulnerabilities/retbleed:Not affected
/sys/devices/system/cpu/vulnerabilities/spec_rstack_overflow:Not affected
/sys/devices/system/cpu/vulnerabilities/spec_store_bypass:Mitigation: Speculative Store Bypass disabled via prctl
/sys/devices/system/cpu/vulnerabilities/spectre_v1:Mitigation: usercopy/swapgs barriers and __user pointer sanitization
/sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Retpolines, IBPB: conditional, IBRS_FW, STIBP: disabled, RSB filling, PBRSB-eIBRS: Not affected
/sys/devices/system/cpu/vulnerabilities/srbds:Mitigation: Microcode
/sys/devices/system/cpu/vulnerabilities/tsx_async_abort:Not affected
By the end of the year I will buy a new PC, but I wonder if I could improve the situation until then. I've overclocked the CPU, which helps a bit.

But my question is, would a newer kernel help? Do they have more efficient vulnerability mitigations?
I'm running the default debian stable kernel (6.1.55), a newer version would be available from backports, 6.4.4.