There can be additional mechanical noise when you hit the limiter, or the fact that the Apexi uses a fuel cut rather than an ignition cut may cause it to ping while on the limiter.
Sam, Alot of us here have spent huge money on our cars, and while we all love cars, I'm sure in hindsight we probably wouldn't do the same thing again. Learn from our mistakes, and invest it.
There is very little margin on tyres, especially R-comps, which there is low volume. Best way is to make friends with a racecar team and get them to organise the tyres for you