I thought AvGas was only 100octane - not much more than your 98 you can get at the servos. However, I think the quality control of Avgas would be better than that for normal petrol - especially after the huge fiasco a few years ago which stuffed up a lot of plane engines.
And, I don't think you can hoard 44gallons of petrol at your home. I think there's a limit, like a jerry-can size or so, but not a large 44 gall container full of petrol. If you live on a farm or soemthing you can do it, but not in suburbia.