I'd be inclined to go either the 5100 or the 7900 route, depending on exactly what you are planning on cutting. If you can get away with a sub-20" bar, the 5100 would probalby meet your needs and, from what I hear, be fun to use as well. If you anticipate spending most of your time running a 20"+ bar, then the 7900 might be a better choice. Either way, I suspect you will be quite content with your purchase.
Although I only cut recreationally, a few days a month, I finally gave in and picked up a 7900 from TonyM (a sponsor on this board) a few months back. The saw has been a pleasure to use - powerful and very light for its power, with excellent anti-vibe. Everybody who has used it has been impressed. And the price was great, too. The only drawback is that I don't get to spend as much time cutting as I did before, because it is so much faster than the saws I had been using. I highly recommend it.
In any case, you should talk with TonyM.
