A quick answer with no speculation.

For 6G V6 and I4 87 is what it's tuned for. Putting a higher octane in can actually hinder performance. Octane is in essence a chemical retard, since te accord has no knock sensor it doesn't try to advance it's timing to take advantage of the higher octane thus actuall hurting your performance since the fuel can't completely burn. I'll see if I can fnd the artical R&T did running 20 cars on 87 and 91 and posting the dyno results. The 6G AV6 lost about 6whp by going from 87 to 91. That difference could be condition related(different temp, humidity, phase of the moon), but it most certainly doesn't benefit you from running higher octane. For a 7G V6 there is now a knock sensor and has shown to take advantage of up to 93 octane, almost a 12whp increase.

No matter how crappy the gas was I never once had the accord knock and that was with almost every bolt on I could get my hands on. I miss the HELL out of 87 octane. Before I got a custom ECU tune I had no choice what so ever in the rex, it's 91 or she got VERY angry. Even a marginal tank of 91 would make her angry, the only way to make her completely happy was to add some torco accelerator with every single fillup(I use 1/4 bottle every fillup at $20 a bottle), with the price of gas and the torco, fillups SUCKED. If I didn't put the torco in I'd have to baby it to make sure it was decent gas, otherwise I'd the magic bb sound and pray I don't blow it to hell. Thankfully my tuner knew what he was doing and I have a rock solid 91 octane map, and a 100 octane map too(some day I might do a C16 map, but she's plenty quick for now)