As an update I am targeting the 912is Sport right now.
As most of you know the bing carburetors do do a fairly good job of altitude compensation until you hit main jets at high power levels which are not compensated and will be more rich.
With EFI this is less of an issue and even with the Bing carbs you could fly for a lifetime without having this be an issue...but we all have our own personal minimums and levels of acceptable risk.
Technical reason for those who care.
Bing CV carbs are almost certainly altitude compensating better than most pilots but only to about 50% of the optimal mixture due to Bernoulli's equation. So the higher you fly richer the mixture will get even at power levels below 75%. I am conservative on this topic but it is important to remember that on Bing CV carbs altitude compensation do not change the mixture the main jets.
With the warning that you should take these following numbers as examples and not as set in stone:
idle to ~ 25%: Idle Jet
15% to ~ 80%: Needle Jet
65% to 100%: Main Jet
Note: As the main jet is not altitude compensated on the Bing 64 CV carbs the mixture will be richer above ~75% than below
(IIRC).
If we choose those random numbers of 100 % at 100' MSL and 75% at 7000' you will be producing somewhere around 60-65% or less at full throttle with a sea level sized main jet. The important part is that you should expect more power loss at takeoff power in any Bing CV equipped engine than you see lower in the power band.
To be honest isn't a huge concern if you plan for this additional drop in power on the top part and/or an occasional visitor.
The Bing CV carbs are probably safer than the problem of pilots failing to lean the engine for maximum RPM at altitude with a mixture control. But remember that a nice idle or acceptable if larger cruise fuel burn doesn't mean you will have the same performance at the top end when the main jets are the largest source of fuel.
The additional weight for FI and x340 is what drove my decision when I cataloged what I would want to typically take on a weekend trip. While the x340 would have more than enough power even rich I think that trying to lean to maximum RPM at full throttle during runup with 180HP on the front on the carb version would be a bit past my comfort zone in a light taildragger too. I am making no claim as to if there is actually at risk of a nose over but it is beyond my personal comfort levels.
As a reminder, this post is opinion and very specific to my decisions, desires, and wants so once again take all of this with a grain of salt. Hopefully this will help others decide to look into this themselves or possible remind people that they need to leave some head room for larger power losses at high DA with Bing CV carbs at high power settings.
Obviously if you only fly at altitude changing the main jet would also be an option as long as you remembered to be careful at lower altitudes where you will be too lean.
For the vast majority of people using Bing CV carbs a small increase in fuel burn is probably the only result of this behavior. For those with engines and a mixture knob remember to lean for RPM during runup above 5K MSL or AD.