5 Point!
I installed a Crow 5 point system in both seats of our RV-6 after reading an accident report where the pilot reported being forced to park a -6 in a trailer park. When the noise stopped, he was in the baggage compartment. I never learned if his seatbelt was still fastened, but this accident is what prompted me to add the crotch belt attach points and the 5 point belts, aside from doing aerobatics. Vans makes kits for the center attach points, although there’s no kit specifically for the -6 and I had to tweak a -7 kit for our airplane. The 5 point belts feel a whole bunch more secure than the 4 point. Anyway, to answer the question, a 4 point is pretty much OK for gentleman akro, but if you’re changing a harness, this would be a great time to add the antisubmarine belt. My humble opinion.