My opinion would be based on the fact that decent blades are quite difficult to get in the 216mm/8" size as it's always been a size for site workers and hobbyists, whereas they are plentiful in the 250mm/10" size as these are used in the woodworking industry. Decent saw blades make all the difference to the end product so having a large range to choose from so that you can find the ideal blade with the correct geometry for whatever you're undertaking is very beneficial. For example, Scott and Sargent have 5 blades to choose from in the 216mm size, if you write off the very expensive PCD blade that's £300 you're left with 4 blades of reasonable quality with various tooth counts, whilst in the 250mm size group there are 38 different blades, even if you write off the most obscure and unapplicable ones you're left with 32 blades, and this is common across all vendors.