Well, of course, neither the Tiburon nor the Sirrus Pro (both around $750) are, strictly speaking, road bikes. They’re more like high-end “city” bikes聴mixing mountain-bike-style frames, handlebars, and geometry with mostly road touring components. These are nice bikes; good for commuting and running errands, but not bikes you’d care to spend many hours riding on the road. Too much wind resistance, and not offering much of an improvement over your mountain bike. Heck, you could just get a spare set of wheels, mount slick tires on them, and use on your mountain bike for those commuting or fun days. Be darned near as good as a Tiburon, and a lot cheaper.
I think what you want is a road bike, my man. Something that lets you get down on the handlebars, lower your head, and generate some speed. In your price range, look at the Giant OCR3 (about $650) or OCR2 (about $850). Both have nice, light aluminum frames and a good quality mix of components (the OCR2’s are a little better, hence the higher price). Both are fast bikes, but have triple chainrings for more relaxed riding when you hit a big hill. Fit either with a luggage rack and you can change into your work clothes at the office.
The alternative is to get a true touring bike, not so fast on the road, but still faster than a hybrid and suitable for commuting or light touring. A good choice is the Bianchi Eros. At $1,000, it may be a touch expensive, but it’s the time of year when you can get good deals as bike shops unload inventory. So, if you find one, make them an offer.