anyone have the stack and reach numbers for a 2011 tarmac. I'm currently on a 56 Litespeed Icon and was thinking if a 54 cm tarmac would fit me. Is the SL4 going to be too low? I am 179cm with a 33 inch inseam.

SL4 geo according to:
http://www.pacosbike.com/product_info.p ... s_id=36066" onclick="window.open(this.href);return false;
stack and reach 543 and 387 for 54

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I think the 2011 tarmac has a taller HT.

is stack/reach more important or top tube length. the difference between TT lengths is 17mm between the 54 and 56 but the reach difference is only 8mm. The shops says its a difference of a 2 cm stem between the 2 bikes. I'm currently riding a 56cm Litespeed Icon with a stack of 551 and reach of 391. After adding the Chris King headset it seems the 56 cm Tarmac is still lower than my bike. Which bike would fit most closely?

Stack/reach tells you more than just top tube length. Add seat tube angle to top tube lengths and you have similar tools. as with any tool, you have to know how to use it.
I haven't checked the sizes of the sl4, but I assume the seat tube angles are close or equal. Then, as with any bike, when the head tube gets taller, the reach measurement is naturally shorter. If the head tube angle was 90degrees, then stack would not affect reach. so you are looking for a certain reach measurement, at a certain stack measurement. Having the right reach at the wrong stack is NOT the same.
With top tube length, a frame can change seat tube angle, affecting overall reach of the bike without one realising it. And it does not tell you how high/low the bars can be.

Seat position is a different measurement from stack and reach.
You always set your seat to the same position in relation to the BB, or you should. You have to select a seat post with appropriate setback to allow your preferred position so assuming you will be able to achieve that position (highly unlikely that you wont be able to), that leaves stack and reach as the appropriate variables to consider for frame fit regardless of seat tube angle.

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