I have owned a D-700 and D-710GA and currently have an FTM-400 in the truck. Both radios are great for APRS and FM work. For me, I found the tedious method of entering APRS messages on the D-710 to be frustrating. With the FTM-400 and its touchscreen, this makes it much easier.
The only drawback to the FTM-400 for me is that the internal TNC cannot be accessed from an outboard computer. The D-710 allowed me to hook up to it and use the 1200 and 9600-baud capable internal TNC to run packet or access the BPQ-32 BBS port I ran on 70cm.
Both radios feature stable output, crossband repeater function, and paging capability. The one addition that I like on the FTM-400 is System Fusion. In some of the fringe areas on simplex, YSF can help make the contact. Also, the Group Monitor function while using YSF is great for mobile position tracking without APRS. This comes in handy for those of us that use it for Skywarn operations and move around to better vantage points.
So, you have some fine radios to work with now! Best of luck!
73,
Korey-WA5RR