1 7/8" may be best in my opinion of the two choices for your application at or near 32" to 35"long . If the 1 3/4" pipes are real close to 30" they will perform very well in your application if you like torque and mid range horsepower. You have a lot of engine and RPM you plan to run, it will likely enjoy the shorter length of the two. Do not go shorter than 30", short is 30" long is 37" for your reference. The 1 7/8" will run better in the upper rpm range. Lots of racers in your sport change the pipes to suit the track they race on. Bigger for longer straight aways and shorter or smaller for shorter tracks.