https://www.specialized.com/us/en/bc/...01&scname=Road
https://pedalforce.com/online/product...902800caa22be3
^ Geometry listings.

As of right now, I own a 54cm 2011 Specialized Allez with a 100mm Stem with the seattube length (including seatpost) at 70cm.

What size stem would I have to transfer to if I went with a 50cm Pedal Force CG1 to have the same sizing as the Allez.
Allez-------------CG1 (50cm)
54.8-------------53cm------top tube length
70---------------71cm------seat tube length (includes seatpost; CG1 is ISP so I cut 1")
14.5-------------11.5cm---head tube length

id consider the 53.

Thats what I will probably go with, but if I bought a 50cm...how long of a stem would I have to end up buying?

Probably 120 if you are setting the handlebars at the same height, maybe 110 if you're going to set them much lower. Are you planning to use 3cm of spacers with the same angle on the stem?

Noooo. Slamming the stem. The Allez has the cone and zero spacers and the only reason it is like that is because I can't find a smaller cone.

Due to the difference in head tube length, I was thinking of a 120mm stem at the same 6*, but flipped up instead of down (though I give it 5 seconds after posting this of someone saying flip it)

the 50 also has a 71.5 degree head tube angle. id stick with the allez.

The 53cm PF is very close to the Allez for stack and reach. The PF is about 1cm lower but the same reach, 385mm.

The 50cm PF is 34mm lower on stack but only 3mm shorter on reach compared to the Allez (even shorter if you match the stack with spacers). Go longer on the stem if you are going to slam it. But if you want to keep the bars in the same position then 110 is about as long as you should go.

Yeah...im just going to go with the 53cm haha. Thanks everyone!