The 5.0 build will most likely come without any of the same UI issues that the 4.4.2 G3 builds have... Actually, I'm pretty sure of that. They've already fixed the UI problems, its just that everyone hasn't had the right build rolled out to them yet. I loaded the CloudyG3 1.1 ROM, which is a multi-model ROM based on the international 10M kit and it runs substantially better than the T-Mobile 10M variants I've tried.
So its fixed.... and 5.0 will most likely be even more improved.
As an aside.... The 'lag' isn't so much lag as UI optimization issues. Screen transitions are a bit jerky, windows scroll quicker than the content renders. Quirks in the underlying framework that are unavoidable on a brand new hardware AND software platform. It's not horrible, and depending on how old a phone you came from, you might hardly, if ever notice. But if you hop on a Nexus 5 or an HTC M8, or even (better) run one of recently released custom ROMs that are AOSP based (CM, AICP, PAC, Liquid Smooth, etc). Back to back, there's a difference.
But..... again... LG has figured most all of those interface problems so I wouldn't suspect any problems with LP