No professional intent means not more than one lens??? I just have to ask.
Anyhow, these are both great cameras, but quite different from each other. I do agree that if you decide that you will only ever need an 80mm lens the Rolleiflex wins hands down. It's much lighter, more quiet and it will produce great negatives. But it's a fixed lens camera and not a system. Now, you will get a very good -flex on your budget.
(As a side note: If I wanted to get a single lens medium format camera I would try to find a Fuji SW690 with a 90mm lens. No ground glass, but a very flexible and capable camera. This is much along the thinking of Tom H. with his Mamayas.)
Within the budget is also a semi-old (read -70ties) Hasselblad system. A 500 c/m housing, 1-2 film magasines, a standard 80mm lens, a 150mm lens, and possibly also a 50mm lens can be within reach if you a little bit patient, as it's a buyers market. It's a larger system but still not very "professional". It will do very nicely with portraits, street and landscape, giving you all the flexibility you will need.
For myself I used a 500c/m with a chrome 80mm and a single magasine for a number of years and found that to be enough, even though I sometimes wanted that 50 or 150 lens, which I didn't posess at the time. My system is larger now, but still the 80mm finds the most use (...ehh, along with my SWC which I bought for US$ 1200, but that's another story). If you want to go a bit wider from time to time, or like to use a long lens for portraits or distant landscape, there you go.
The optical performance of most of the Rollei lenses is very good. The "top of the line" should be the Zeiss Planar, which of course is the only option for the 'blad. Now, in practical terms there is no telling apart the different Rollei lenses, especially if you stop down a few clicks. An MTF chart would probably tell the difference, but that is not my normal subject in front of the camera.
Anyone of these cameras will, given proper use and care, give you a piece of engineering that is capable of breathtaking results along with that confidence which comes with great camera design and german glass.
It's really down to you to figure out what you want to do with your photography.
//Björn