The geometry is different on these bikes. I would think one should feel different than the other. Its not good or bad just at least somewhat different. I think I would lean toward the Giant because its has more relaxed geometery and espcially the longer toptube (personally I have short legs so I like this) and it also has an alloy fork. The Giant is a longer bike overall. I have always kinda liked the Sirrus line and depending on what you like and your physical dimensions it could end up fitting you better. Like others have said either bike will likely be nice to test out the larger wheel is better/faster theory. The Shimano stuff on the Specialized is nothing fancy so I would imagine the SRAM stuff would stack up to that. I personally like the look of the VIA stuff better not that it matter much. Enjoy the test rides. =)