I was running 89 octane mid-grade all the time until just the last few tanks and was happy with it. However, it sure seems like my VX is actually running a bit better on 87 octane now and I've made no other changes to cause that. Plus the weather is getting warmer which usually seems to take the pep down just a tad, but the VX seems slightly peppier. Not a huge difference mind you, but I think 87 may be better for the non-SC'ed folks. The only difference I really felt with 89 octane was right after fill-up, which had nothing to do with the grade of gas. I think the fact that it has a full tank makes it a little peppier for some reason, but I don't know why. Maybe the fuel pump isn't working as hard then and/or the fuel pressure is increased?