AM3+ is better. Not only for performance, but longevity and upgrade considerations. FM2 simply isn't powerful enough, and doesn't have enough PCI lanes.
The builds you've configured look really good. Only thing that really needs to change is the motherboard. You couldn't possibly use the D3P, it uses a 4+1 power phase. This is insufficient for some of the power hungry AM3+ CPUs. 4+1 is suitable for the 6xxx chips, but not the 8xxx chips. Spend an additional $20 on one of the M5A99X range, which uses a 6+2.
I would go with AM3+, AMD is going in a really strange direction on FM2+ post Kaveri plus AM3+ has more PCI-Express lanes meaning you have more expandability and it also can handle higher end GPUs
Roadmaps are not set in stone, just because its not roadmap doesn't mean it doesn't exist, plus the next FM2+ APU will only have 16 GP PCI-Express lanes (down from the 24 of Kaveri) which is not very good and really nerfs the platform in favor of HSA, which in my opinion is not the way to go
Discussion from a "future upgradability" standpoint
AM3+ Is essentially dead, its been around for a long time, and really is just a band-aided AM2, which was used by Athlon 64's in 2007.
FM2+ is probably dead too but you will most likely have one more generation of APU's. Excavator is coming soon enough, and will probably be on FM2+. But after that, who knows. AMD is focusing HARD on making a new platform....Skybridge. Because of the engineering involved in the interchangeability of ARM and x86 on the same socket, id say a new platform will be coming in the next year and a half.
All that being said-- both platforms will give a variety of upgradable features, thanks to PCi-E. AM3 and the 990FX specifically has 38 PCI-E 2.0 lanes ( it is older technology based on the 790FX from 2007).... but the A88x chipset in the FM2+ platform supports PCI-E 3.0... which doubles the speed of the PCI-E Bus. I can't find spec's on how many lanes Kaveri has (its on the APU, not the northbridge). E
TL;DR i think FM2+ is the better bet for future upgradability. The only thing its missing is native support for PCi-e based SSD's, but you can fit one in a 4x pci-e slot and get good transfer speeds. And Sure you will not have AS MUCH CPU perfromance as an 8 core power hungry monster, but a a10-7850k can play just about any game on low-medium settings on its own, and could run on a power supply <300 watts in an ITX case if you wanted. Or you can add a graphics card, and be with 10-15% of a "better CPU" and still get very playable rates.
EDIT:
WHY ON EARTH DO YOU NEED A 700 WATT POWER SUPPLY ON THAT FM2+ COMPUTER.
And the only AMD processors worth buying for FM2+ are the A10-7850ks or the 7700ks,
NZXT Hale is a good line of PSU. But regarding the FM2 platform, it's better to save the $20. FM2 is only suitable for a single mid-range GPU and a couple of additional devices. You won't use more than 500W, simply.
I also wouldn't personally buy a Kaveri with the intention of buying a high-end GPU in the future(which is why I just bought a 4670k), nor would I recommend doing so to my friends or clients. And I also agree you will most likely NEVER use more than 500 watts, and if you have a more appropriate sized PSU you will save you the money now, and more money over time with gained efficiency.
All that being said, you COULD put a high-end GPU on an Fm2+ platform and be pretty OK, see Jayztwocents for scaling
That's the perfect demonstration. I wouldn't get anything higher than a 270. It's basically the same level of performance as the 270x. Don't need much more than that in most games at 1080p.
I managed to match it with an Athlon CPU. It's got the same approximate processing power, but fewer power saving features and no iGPU. An Athlon 750/760 is the same as the older A10 without the graphics.