well as i said there would need to be sufficient proof that you were speeding, or that high speed was the direct cause for the accident. For Example, if you simply pulled out of a T junction in front of someone and got T-boned and you had a built RB26 with twin high mounts, PFC etc etc etc, clearly it was not the mods to blame, but simply driver error so you would most likely get paid out (pending the insurers descretion).
However, if for example you had pulled out in front out someone but had several gauges on the dash or a-pillar that were obstructing your vision and this could be proved, then your claim may be declined.
End of the day, some insurers are far more lenient than others on issues like mods so its a matter of find the right one.