The advantage of the variable steed normally means that you can spin a larger than 1" diameter bit with out having to worry about the tip speed of the bit being too high. You simply slow down the speed to a safer speed. That said, with a router of that size, you are not going to want to be spinning the larger bits anyway as the router does not have the power to comfortably perform the task and especially on the biggest bits.
That said, this router will be a good size for cutting with the smaller profile bits and a great size for cutting dove tail joints. Variable speed comes in handy regardless of the size bit your are spinning when you work on different woods. Since many woods are prone to burn more easily than others, slowing down the bit speed can help to prevent burns. Also many woods cut better and cleaner with different cutting speeds. So I would recommend getting the variable speed.
Lastly, the current Wood magazine had a review of several routers in this class that come as fixed base and plunge based kits. IIRC Bosch came out on top followed by DeWalt and Makita. and lastly the 690 series PorterCable. If you are wanting to be frugal with your purchase, the Porter Cable is a safe bet but the design is becoming dated and out paced by the competition.