My thinking was that my 64 bit addons would work well in P3D 3 or P3D 4.
There are probably more addons available for version 3 than version 4 due to addon development
taking more time than P3D updates.
I hope that makes sense. Maybe someone who has moved from 3 to 4 could explain how it affected their
number of compatable addons reducing or staying the same after moving. Then I could purchase one or the other
with more confidence.
If you don't already have a bunch of p3D v3-specific add-ons, I'd strongly recommend moving straight from FSX to v4.
P3Dv3 is a 32-bit program that, like FSX, is constrained to run in a practically restrictive 4GB virtual address space. It is marginally less susceptible to OOM errors than FSX because it uses DirectX11, which eliminates the memory load associated with the user-area video data required by DX9 applications like FSX. P3Dv4 is a 64-bit program that is not constrained by any currently practical limit on VAS (theoretical limit is 16 exabytes, and current OS implementations use 48 of the possible 64 bits for a max of 128TB). Because of this, the OOM , and all the programming gyrations and constraints needed to limit memory usage to make the sim and its add-ons fit into 4GB of VAS are history in P3Dv4.
Not sure I understand what you refer to as your "64-bit" add-ons. Sceneries, unless they have active program elements, are just data, and not "32-bit" or "64-bit"
per se. Most FSX scenery that has issues in P3D is due to changes in the format of the data, and that is not a 32 or 64-bit platform issue. Most of the FSX sceneries that I've gotten got to work in v3 also work in v4. Some needed modification, and there are many that were updated for free or a small upgrade fee from the FSX version. Most aircraft need a specifically-compiled version to work in one version of P3D or the other...it makes no sense to me to pay now to upgrade or repurchase an aircraft for the discontinued 32-bit platform.
Moving to v3 may preserve a very few add-ons already on-hand, but at the expense of foregoing use of many of the add-ons being developed now and going forward. The 32-bit platforms (FSX and v3) are largely being abandoned now, with more and more new add-ons being developed only for v4.x.
Regards
Bob Scott