Omega cal. 1040 vs. cal. 1045

I read somewhere that a lot of people prefer cal. 1045 (coming from Lemania cal. 5100) to cal. 1040 (coming from Lemania cal. 1340).
So cal. 1045 (i.e. Omega Mark 4,5) seems more sought after than cal. 1040 (i.e. Omega Mark 4).
I read on omegaforums.net that Omega cal. 1045 has many plastic parts, and I think Omega replaced cal. 1040 because it was too expensive.

What (and why) do you prefer between Omega Mark 4 (cal. 1040) and Omega Mark 4,5 (cal. 1045)?

Thank you

The 1045 and it’s Lemania brethren has a solid reputation with many watch brands over decades. The 1040, as you point out, was expensive to produce and was in production for far fewer years. The 1040 is old school craftsmanship and precision design while the 1045 forged new ground in industrial design for mass production. Take your pick. Both are worthy to be in your collection.

I love the functionality of both movements. Having the chronograph seconds and minutes both on the cental pivot makes reading them far easier. The 24hr counter makes setting the date correctly a breeze.

If pressed, I’d say I preferred the 1040. It seems to more closely embody the precision mechanical design that makes us watch enthusiasts in the first place.

Here are the facts as far as I see it:

1040/1340:
-A first (automatic chronograph) for Omega and Lemania
-Omega got an upgraded, exclusive version (24 hour disc)
-better finishing
-fewer plastic parts
-Omega made a chronometer version that was the first ever for an auto chrono
-Omega only used the 1040 for a few years, other brands used it beyond that but not widely

1045/5100:
-More complications than the 1040/1340
-Omega got a pretty stock version of the Lemania movement
-A less costly movement to produce, including more plastic parts
-Used in a wider variety of brands
-Omega used it for over a decade, other brands even longer
-Kind of a cult following, largely thanks to Chuck Maddox's writing

Both movements have their followings, but to me, the 1040 is more interesting because it is Omega-exclusive, it was first, and it was short-lived. The end of the 1040 coincides with the beginning of the Swiss Watch Crisis, and you can see it play out in theses two families of watches. The 1040s were bold, colorful, and state of the art - symbolic of a company and industry riding decades of success. The 5100 was a cost saving measure and the watches Omega put them in lack color. Not to say that I don't like the 1045s or that the movement is bad, but that's how I see it. These watches are a perfect metaphor to me for Omega at its peak and the beginning of its slide.

Edited my previous comments, thanks!

I think the 5100 has the reputation of being slightly more utilitarian and robust , especially when put under compression shock and extreme g-force;- which is why it ended up in so many military and airforce watches by the likes of Eberhard, Sinn, and Fortis. I have examples of both (in a BWC and an Eberhard) I think the 1340 just edges it for historical reasons.