Moving from Endurance to Performance bike

Additionally, if the OP wants to try the geometry, slamming the stem in a Defy results in a geometry similar to a TCR with the default amount of spacers.

I changed from a Medium Giant Defy to a small Giant TCR in 2011, which perhaps is a slightly different situation as the Giant Defy was too big for me , the Giant TCR wasn't the answer however as whilst the reach improved (10mm less reach, 20mm less stack), the reduced stack put me in a position that I couldn't sustain because of my body shape. (at the time I was regular swimmer, weighted 74kg and did lots of core work at the gym), the right answer should've been a different frame that fitted me properly, it took me until 2015 to work that out! So really, this is a tale about getting a frame that fits you rather than be charmed by aggressive positioning and horizontal lines.

I do have a CR1 SL, but technically that is meant to be a more endurance biased (higher front end) road bike.

I also used to ride Synapses which are out and out endurance bikes, but had a hankering for an aero bike.

The bike I wanted came up for a massive discount, and I went for it - due to the time of year I wasn't going to be riding it for 6 months, so I spent that time working on my position on the turbo, as well as my own flexibility and less so, my core strength.
I'd spend 4-6 weeks in each setup position, before lowering the stem, and or swapping out for a longer one, and ensured I spent plenty of time in the drops.

The hard work paid off, and the new bike gamble worked, as it fitted me, and was until very recently the most comfy bike I owned - and that's only running on 25mm tyres. Plus into the bargain I am now more flexible, and able to ride lower than I could before, with no comfort issues on long rides.

I wonder if your desire for a new bike may be more down to the fact you know that will motivate you to train more, and ride more out on the road.

That's not a bad catalyst by any means, but you do run the risk of it simply not fitting you, or not being able to adapt yourself to fit it comfortably.

I suspect the Ribbles are similar to a lot of high end bikes now, that have integrated cockpits, and proprietary shaped spacers etc, mean that adjusting the position can either be very difficult, and or very expensive.

I took the same gamble with my own aero bike, which has a fully integrated bars and stem, which would have been horribly expensive to change, but I got fairly lucky I guess - it was the same brand at least, and I did spend a lot of time studying and comparing the dimensions between my CR1 and the new frame, and I have also followed this method for subsequent purchases, and it seems to serve me well.

With deep section wheels I can tell it is notably faster than my CR1, so I suspect an even more modern bike with fully integrated cables and better aero credentials would increase that margin a bit.

I'd suggest examining the dimensions of the two bikes at the very least, and as mentioned above try and alter your current bikes position to mimic that of a more aggressive road bike.

If you are still keen on it, and are training hard, looking at FTP for example, you could set yourself a target of if I reach X watts, or X watts/kg then I will place the order.

That has the bonus of hopefully motivating you to train, plus you'll be training in a position similar to that of the new bike, so you'll soon have an idea on whether you can fit the position, could do so with some work on your strength/flexibility, or whether it's a massive no no.

Good luck!

Although it is often possible to achieve the same position on an endurance bike as a performance bike, that is not the complete picture. A performance bike will feel sharper and more responsive to ride, and to mind is just more fun which is why I ride a performance bike. I guess i am lucky in that I am comfortable in a racy position and can ride all day, which is not to say that I am fast, just flexible, not everyone will be able to hold such a position for long.

Imposter is right though, you will be lucky to measure any difference in speed between a performance bike and an endurance bike given that you ride both in the same position.