Over the holidays, I will be able to look at and use my brother's 10" I3V right next to my 8" . I hope I'm wrong but I suspect the 10" is not as well engineered. There's more to enlarging something than just adding an extra 50mm to x, y and z using all the same materials.

for example, I think cheap windowpane glass and the PCB heated bed work well at 200x200mm. I think it may be too flexible/wavy at 250x250. I do know from my brother that the 10" has had more difficulty with bed flatness and Z bed level consistency. Over the larger size i suspect the amplitude of the irregularities is significantly greater. The larger size machines/parts haven't been made as long so there's less end user feedback.

If you don't mind being an early adopter and going somewhat experimental, then by all means go as big as you can afford, it's quite cheap to double the capacity of the printer. I tend to like a mature product and haven't needed to print something big yet, so I'm ok with the 8".