Specialized Allez and Specialized Sirrus have very different geometry and 2 models of the same size fit very differently
Sirrus feels short and tall with very long upright head tube
Allez (similar geometry as the carbon fibre Tarmac) feels long and low with short head tube
I own a Tarmac and a Sirrus. Sirrus has mudguards and is used for wet weather riding and wet commuting.
Tarmac for proper road riding and dry commutes when I need to go fast
For the Sirrus I have cut the fork steerer to minimum height, removed the taper headset cap (which is a cover for the flat headset cap underneath) and used a BG Stem set at -16 degrees, all in an effort to get the handlebar as low as possible due to the long head tube.
Its not as fast as the Tarmac due to the more upright position (you feel this going against wind) but its comfortable and great for cruising at a relatively fast pace. Bike is 9.4kg with mix of Tiagra and 105 and road wheel / tires and carbon seatpost / bars / saddle
I’ve converted a good number of drop bar road bike to flat bar bikes for customers who just could not get on with the drop bar positions.
Its not cheap but they all seemed happier afterwards with most commenting they actually rode their bike regularly, which was not the case when their bikes had drops.
Specialized also sell a couple of high end mens (sirrus) and womens (vita) models which actually use the Roubaix and Ruby carbon road frames fitted with flat bars and flat bar shifter / brake levers as stock