MerloobiI got both and I consider the 800 more portable than the 600, due to the retractable tip. The 600 is nice for writing at a desk, but running between meetings or putting in your pocket the 800 is the way to go.
From writing feel and build they are very similar (only differences are due to the retractable tip).
So, it all comes down to how you plan to use it. I'd say get the 800 because of the versatility, but that's me.
So, it all comes down to how you plan to use it. I'd say get the 800 because of the versatility, but that's me.