275/40/17 is about about 25.66" diameter? I tried to run a 245/40/18 (25.72") in front with stock suspension and the tire was too tall and hit the OEM suspension lower spring perch in front. Unless that front wheel is pushed way out (and with a 17x10" it would be out there a ton!) that size may not fit up front. I have got a Maxxis RC-1 in that size I run on my Cayman in rear, I can try to put it up front on my Boxster and see if it clears that perch (unless you already tried it). It might be close!
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