Thanks for the reply. I was probably trying to keep it a bit simple, but i can definately expand further on my measurements.
My inseam is 84cm.
My saddle height from the BB on the Cervelo is 72.5cm. I have been fitted several times and people try to put me up another 1cm but it causes me all sorts of strife.
My current cervelo has a 90mm stem +6 degrees and i also ride the FSA Compact Bars so as to have a shorter reach/drop. The head tube set including spacers measurers 22cm.
The Ridley i test rode has a 110 mm stem + 6 degrees.
I think your correct about the taller top tube making it more comfortable. Just so we are clear, whilst i have said i felt comfortable on the Ridley my thoughts were that i would have to still put on a shorter stem and have some type of compact bar on the ridley.
When i said 73.5 degrees i was referring to the head tube angle. The STA is 73 degrees.
The HTA makes almost no difference at all in the reach - usually on the order of 1-2mm per degree, compared to 8-10mm per degree for changes in the STA. It's the seat tube angle you need to watch for significant differences.
When you're test riding bikes, they should be setup as closely as possible to your current ride, or you get false impressions. Bars that are set a lot higher can allow you to tolerate more reach, so that's not a surprise that the Ridely felt comfortable.
Just to empahsize the difference in your setup to mine, I'm only 168cm tall (7cm less), but my inseam is only 1cm shorter and my saddle height is 1cm higher, at 73.5cm. Your saddle height definitely seems low, but not excessively low, if you pedal with a relatively horizontal foot. Raising the saddle 2-3mm at a time over a period of several weeks might be worth trying.
The reach on a 54cm Cervelo is nearly the same as my 51cm LOOK 585. I use a 110mm x 73 degree stem with a saddle to bar drop in the 11-12cm range, with short reach bars. I've also got a long railed saddle pushed nearly all the way back with a 25mm setback post.
IMO, if you've got to use a short stem and short reach bars, the frame is too long for you. You would need a small sized Ridley.
If you can't tolerate very much drop from the saddle to the bars, consider a change to your saddle fore/aft position. The further back you get, the less weight on the hands and better balanced you will be over the saddle. This can make both more drop and reach tolerable. It's common to move the saddle forward or use a short stem when the reach feels too long or low, but moving the saddle forward is the often the opposite of what really needs to be done.