Depending on what type of carpet you have, a Convertible will clean either just as well or better than your Eureka. You will not be disappointed. The noise and sound depends on which period the machine was built in. The later 5amp models and 6amp Guardsmen are a bit loud; nothing compared to a Concept or Elite but a tad noisy. Hoovers have a low grumble noise, while Eurekas have a higher-pitched whine to their motors.

It is a very hard decision to choose a bag set-up. The C bags are single-ply, leak dust when you replace them, and clog easily. You can get a newer A-bag model, but then you get a cheaper plastic base and often duller aesthetics. The C bags are not terrible, but get annoying with regular use. If you want to use a Convertible daily, get one that uses A bags. Otherwise, the metal-base models up until the late 70s are the way to go for collectors. But choose what you want, that is what is most important. 

One thing that does bother me with C bags is that they look almost the same inflated then when the machine is off. There is no ballooning effect like on a Kirby or the A-bag models. I know that doesn't matter to everybody, but it is something to take note of. 

Either way, you will love any Convertible you get. They really show why Hoover was #1.