Hi Bugsy,
If you are working on a large game, it may be as well reverting the build so you can complete it (I created a rollback version called public-release-lastdx9 which you can use to get your old public build back). Best way to do that is to back-up all your projects and assets in the current installation, delete the local folder and then go to Steam and rollback to the above version. Then you can drop your backed up files and you're back to where you were.
If you did want to get your project running under the new DirectX 11 engine, I can help with that no problems. As you can imagine swapping out an entire graphics engine is bound to affect larger projects, and I tried as much as possible to use the Public Previews to catch most of the gremlins, but we will not have caught them all.
If you're up for it let's tackle these points first:
3. abysmal editor frame rates
4. lightmapper seems "completely broken" for lack of a better word
For the editor performance, if you open SETUP.INI and change "disablesurfacesnap=0" to "disablesurfacesnap=1" this will speed up the positioning of entities in your world. Whilst in there, you might also want to change "PBRoverride=0" so you can keep using the legacy shaders and DNS texture system.
For the lightmapper issues, could you create a small FPM of a level (ideally using stock media so don't need to send me custom media) and lightmap it and let me know what the issues with the lightmapper are, this way I can reproduce at this end.
Also, any smaller issues you come across, just post them in the issues tracker and they can go on the list to be fixed. Here is the link:
https://github.com/TheGameCreators/GameGuruRepo/issues
As one of our best GameGuru developers, I want to make sure you can continue creating cool games, and I am sure that the new DX11 engine (suitably tweaked) will be a benefit as there is a lot crammed in there since the version from last May. Also, if you wanted to send me your entire game project and files, I can run larger scale tests for you and reproduce what you see (and get them fixed).
PC SPECS: Windows 8.1 Pro 64-bit, Intel Core i7-5930K (PASSMARK:13645), NVIDIA Geforce GTX 980 GPU (PASSMARK:9762) , 32GB RAM