Just trying to find out which is going to be stiffer and offer better shifting, a braze on front mech with a carbon clamp or a built in clamp on front mech ?

I'd say that the forces involved are relatively small and that it doesn't matter at all

If it's a "braze on" then the stiffness is going to depend on the way the manufacturer has dealt with it.

I note that Campy has had to introduce a stiffening gizmo because on some frames the braze on is not stiff enough to handle their EPS FD.

My view is that a clamp on system is probably more reliable, and offers better adjustability too.

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Always hated the clamp on. It marks up the frame. Braze on! BS on that stiffness bit.
If the frame can't handle a front derailleur then that frame is not worthy of components.

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Cervelo's "braze ons" come to mind as being particularly awful.

If building up a steel or ti bike, go with braze on. Same if the mount is integrated into a carbon frame's mould. Otherwise, you don't have much choice. Shifting on a clamp-on style front derailer will typically be a little better than using a braze with lightweight adaptor if your rings are problematic. However, I'd wager a braze fd with a parlee or k-edge adaptor would be a bit lighter.

Clamp-on derailleurs mount very solidly. If youre going to be using a carbon clamp, however, youre removing the clamp-on derailleur's one possible benefit. Braze benefits mostly revolve on not requiring the seat tube to be one of three round sizes. The seat tube also no longer has to bisect the bb. Many companies pay too little attention to fd mounting stiffness and adjustability, although more and more are waking up.
A side note, why doesnt shimano include the fd support setscrew of di2 derailleurs on mechanical derailleurs? They would certainly be a benefit on some bikes w weak mounts.

Won't dent your CF seat tube w/ a designed-in braze on bracket. (friend's Super Six dented @ FD clamp location)

I went from a clamp on Record to a braze on using a Parlee carbon adapter. I really can't tell the difference in shifting but it is lighter!

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I don't think it matters much;
But I notice that on quite a few carbon frames, the "braze-on" tab is really a "pop-rivit-on" tab. In those cases I think clamp on would be more reliable and secure.

On my carbon colnago frame the braze on has 4 pop rivets. It not going to go anywhere.

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No brazing torch involvement, so I'll vote for the "integrated clamp", since it's lighter and looks better.

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Cervelo's pop-rivet braze on hangers are awful. I have one on my slc-sl and it is FLEXY but my r5 has a molded carbon one that is very stiff and solid feeling .
Like socratease said, braze is lighter in most cases and can be stiffer if done correctly! If you run rotor or other elliptical chainrings, especially in large gearings like 54+, sometimes the braze on hangers don't have enough adjustment however. Same thing if you feel like running CX 36/46 gearing on a road bike (I don't know, just an example that I've tried!) - where the adjustment of the braze on is normally limited.

I doubt that the 54 chain ring would be a problem for a braze on.
Maybe a 60 tooth.
Also it would not be good to have braze on on ultra thin tubing walls.
For those a clamp is better.

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I never took drugs to improve my performance at any time. I will be willing to stick my finger into a polygraph test if anyone with big media pull wants to take issue. If you buy a signed poster now it will not be tarnished later. --Graeme Obree

Stella - I experimented with a 53 t rotor ring a while back to a 7800 front d and had to dremel a little material off of the braze on as I couldn't get the derailluer to sit high enough to clear the rings (eliptical, not round)... Can't quite remember what bike it was on - I think my Cervelo scl-sl but not sure. I don't think Sram front d would have this issue as they come with two mounting bolts for the front deraill and thus have a lot more adjust ability.

Thanks. My experiences were with round rings only.

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I never took drugs to improve my performance at any time. I will be willing to stick my finger into a polygraph test if anyone with big media pull wants to take issue. If you buy a signed poster now it will not be tarnished later. --Graeme Obree