I benchmarked the LC III earlier comparing 7.1 with 8.1 using Speedometer 4.0.1. Here are the results (winning scores are bolded):

7.1

CPU: 0.432

Graphics: 0.376

Disk: 1.827

Math: 1.498

8.1

CPU: 0.431

Graphics: 0.371

Disk: 1.771

Math: 1.503

In 8.1 math was slightly faster but disk performance was down. Which was surprising as the article that inspired me to run the Speedometer tests said it was up to 30% faster in 8.1. But then they were comparing it to 7.5.5 and not 7.1.

Still there isn't that much between them after all.