The difference between pump 91 to pump 93 and being able to run e85 will be a huge change. About 10.5 to one with aluminum heads is considered about as high as compression should be for e10, or pump gas. E85 on the other hand can tolerate much higher ratios. For e85 out of the pump, a race motor will tolerate 13/1, and e85 race fuel or e98 ethanol can be run at up to 15/1 from what i have read. So if you can dedicate an engine combo to e85 it will be able to handle some serious compression . I have a 2019 5.0 gt mustang with factory 12/1 compression, and after retuning it for e85 the difference was huge.