Clarification on tuner for calibration please

[Kllrbee]

Im thinking of finally going to 315s from my stock 285s on my JLR. I understand that a tuner of some sort would be needed to recalibrate the speedo/odo. Ive used tire size calibration calculators and it would be off by 5%. So showing 40mph would actually be 42, 60 would be 63, and so on. This doesnt bother me as Ive dealt with that on many other trucks and Jeeps in the past. Ive heard that its more important for the auto tranny to adjust shift points, essentially putting you back into the proper power band. Since I have a manual, that shouldnt apply to me. Is there anything Im missng here as far as a drawback to NOT recalibrating?
If I NEED to get a tuner, I will I guess. Just seems like an unnecessary expense if only for recalibration that wouldnt really affect me.
Thanks for the help and advice.

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[Monster1926]

Miles will be off on the odo overtime. I just recalibrated mine with ECRI pretty cheap $130 ish total ($84 for the module and $50 to access it) and easy. If they were shitty I’d be honest. It’s not married and you can use it on any jl just pay the $50 fee and your good to go.