ive been in one of the guys on briskoda with a 500Hp mk1 stripped out vRS with diff and R888s on the front with pilot sports 2s on the rear and it wasnt bad at all.
pretty much all the track days in my vRS have been done with mixed tyres. originally had exaltos all round.
wore out the fronts, fitted toyo T1Rs on the front and let the exaltos on the rear. the result no issues.
put the toyos on the rear fitted vred sessantas to the front. the result-no issues.
granted R888s have a big grip advantage, but each of the above front tyres were large improvements in grip on the tyres they replaced.
TBH mike you only paid £150 for the toyos. For that price id stick em all on and use them for the summer. then replace them tax free later.
but if you want to just use them on the fronts, do it. ive been in the car with you, you dont drive like a tool, so i dont for'see that much of an issue provided that you remember you are running this tyre setup