Onder

I did some conversions and some math and here are numbers with which you should be confident:
Pad Y 609mm & Pad X 523mm (this is to the center of the pad)

There are two ways you can go - as you are already aware...

2019 Canyon Speedmax SLX, size small, long stem, pads one hole back from the furthermost mounting position and 45mm of arm pad pedestal. You can do that configuration with either the flat bar bar or the rise base bar.

---or----

2019 Canyon Speedmax SLX, size medium, short stem, pads one hole back from the furthermost mounting position and 15mm of arm pad pedestal. Again, flat bar or rise bar.

You asked me specifically a few posts ago this: .....
You asked, so here goes - I don't participant in the rabid belief/fascination/obsession our industry (and this forum) has for aerodynamic-ness. Yes, there's value in being slippery - yet it seems to me nearly everyone ignores the dozen or so priorities that MUST precede aero (training accurately, not being fit properly on the bike, not being skilled enough to pedal through corners or down a hill, carrying too much body fat, poor pacing, etc. etc. etc.) This is why we see venerable people (read: old) on modest bikes (read; shitty) with durable wheels (read: boxy & slow), with antique groupos (read: 9 speed), with ironic cranks (read: long), comfy helmets (read: vented) - crushing the bike splits of younger people on $10,000 bikes with disc wheels. There's a ton of stuff that matters before aero and then the aero gains are so easily erased with goofy, foolish actions.

My guess is that if you put a size small Speedmax in a wind tunnel and tested its drag against a medium, the small would beat it. I think this is true of all makes/models - And I think that matters for one person: Lionel Sanders and nobody else.

Here are the logical considerations to take into consideration between the two bikes:
1) Room to Move - by this I mean does one bike paint you in a corner in anyway. As it happens I think this might be the case here. You currently ride with a handle bar elevation (drop) of 114mm. That's ~15% of your saddle height, pretty sizable. You speak of having this bike for ages and I think you, like many of us, will find as you age you'll want to reduce the ol' neck crane and you might soften that drop to 110mm or 90mm. It's important to note that the small bike will only move 10 more mm - AND - you'll have to acquire an aftermarket item (high stack flat spring) to do it. The medium will let you move 30mm in that direction if you so desire. Also, if you ever want to go longer in your cockpit the small will dead-end in 4mm and you'll need the aftermarket TSP item to go longer.
2) Stock comfort - I've already noted the TSP and high stack flat spring - it's good to consider the elevation difference between the aero position and the pursuit bars (bull horns). The bike comes stock with the flat base bar. If you get the small the distance from the arm pads down to the brakes is 45mm for you. It might be nice to pruchase the rise base bar so that the brakes are in close reach from the aero position. On the medium there's 15mm of gap there and, for triathlon, I think that's better.
3) Availability - this is no joke. I started this thread on November 21st of 2018 and there were ZERO SLXs available then. There were no SLXs available (in the US) until February 23 and for the first 10 days after that only size medium. As I type this there are S, M, and L in the 9.0 and M & L in the 8.0. How many? Who knows. When's the next batch coming in? Who knows? I don't know and I've asked important people who seem unwilling or unable to tell me. So sometimes choice is about what's available.

If you've got more questions - bring 'em.

Ian

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Ian Murray
http://www.TriathlonTrainingSeries.com
I like the pursuit of mastery
Twitter - @TriCoachIan