Rack performances on 2020 iMac GPU: any opinions about 8GB Radeon Pro 5700 vs 16GB 5700 XT?

Considering a new 2020 iMac and wondered if the 16GB Radeon Pro 5700 XT would make much of a difference compared to the 8GB 5700 in terms of Rack performance.

This is my work machine so Rack is not the only consideration but would be interested to know if anyone knowledgeable about these things can chip in?

(CPU would be 3.8GHz 8-core 10th Gen Core i7)