I previously asked you about revs at 80 mph, out of curiousity. The 350F is not a high revving bike nor does it has much horsepower. It is a fun bike to get around on in town, and you know the saying, it is more fun to ride a slow bike fast than a fast bike slow.
I was curious because you obviously don't want to strain the engine to its upper limit and just keep it there for extended amounts of time. 20 minutes isn't terribly long but you don't want to pin the throttle on a small bike for extended periods of time. Believe it or not, this query was made out of curiosity and concern for your engine lifespan. Have you done any engine work to the bike?
By contrast the 750 has about double the horsepower, but it is a heavy bike. Not too heavy for your size. Given your height, you should be able to handle the weight fine. You don't feel it as much when the bike is rolling, but it is NOT as nimble as a smaller displacement bike. It is also much more top-heavy. That said, guys at your height are a bit heavy for a 350, even if svelte.
You should think about graduating to the 750. It is by no means fast by modern standards.