There is a lot that you can do to make your Sirrus feel significantly faster. Lower your bars as much as possible: spacers to the top of the stem and flip the stem. Specialized has the nifty stem that you can get four different angles on to play with (if you have the labelled tapered collar). That one is free.

I put almost $800 in upgrades in my Sirrus: road crank, SRAM X9 drive train, better wheels, ergon grips, and would ride tucked as much as possible, but still not as aero as a road bike. The best seat to bar drop I could get was about 1.5", as I have an XL frame for my 6'3" self. This spring, I bought a smaller frame with shorter stays and track bike geometry, moved all my good stuff too it, and definitely picked up some speed, but only like 1 mph on averages. And this is with a 4.5" drop seat to bars.

I really don't know what you would get as a whole bike in the $800-900 range that would be dramatically faster. You will definitely corner faster (better cg positioning) and be more aero, but everything will have crap wheels, and tiagra shifters (which everyone says you can't shift from the drops).

Might want to look at $3-400 wheels and some 23 or 25 tires. Would make it feel and roll much nicer. I did the road crank first cause the top end wasn't there as OEM, but that got complicated (mtb FD doesn't like road crank, likes to drop chain).