I wouldn't recommend rewiring either arm unless there is a problem.
The 309 already has silver litz, and the 3009R is worth more in its original condition.
As far as matching to your 16g Benz LP, the Benz is at the weight limit of both arms.
Max cartridge mass on the 309 is 17.5g
Max cartridge mass on the 3009R is 27g.
The effective mass on the 309 is 9.5g
The effective mass of the 3009R is 12.5g
Based on specs the 3009R should be a better match ( assuming it is in top condition ).
Sound wise the 309 will sound more precise, more grip due to the gimbal bearing design, the 3009R less precise but also less mechanical due to the knife edge bearings ( very free ).
Best choice will be very much dependent on your overall system balance and your preferences. They are swings and roundabouts in performance.
If you are looking to upgrade a real option would be to sell both arms and buy a better one.