We run the M/T 3062W. The W is for stiff sidewall tire. The next size down from the 3068W your liking.
We've put almost 500 passes on them over 3 years on a 10" rim and there amazing. This weekend in Fontana, Calif. temps from a low of 103 and high of 111. Track temp from 130 to 145. In nine passes car ran from a 7.211 to a 7.196 1000' numbers.
We just got a new set of the 3062W to run on 12" rims. Ran them one tnt & race in LV so far. Race was called after 4th round because it was cold and guy's were having a tough time getting down the track. Our 3rd (left lane) & 4th (right lane) round wins were the exact numbers to the 1000'. 9th & 10th pass on new tires.
I went with the 62's over the 68's because of the shorter sidewalls, for less movement. Same as stiff sidewalls, less movement.
And throw gear at it to make her happy RPM wise. The 62's put a lil more tire on the ground and weight less. 12" rims this time around puts a extra 1/2" of tire on the track and will have less tire growth to control it.
You'll like the 68's and more importantly the car will. just keep her on jacks when resting