STDA4000200 vs. STDA4000100, no idea. However I suspect aside from whatever regulatory paperwork is different between USA and Europe, they are identical. http://www.storagereview.com/seagate_backup_plus_fast_portable_review Shows two Samsung 2TB M9T 2.5" drives inside. Per: http://www.storagereview.com/samsung_spinpoint_m9t_hard_drive_review They smell like conventional PMR drives.
There are ample articles, both on Storagereview.com as well as other sites, discussing the difference as you noticed. For reads they appear to be identical, it's only for writes beyond one zone's worth or whatever (25GB I think?) that they get slower. I don't think any SMR-based drives have been around long enough to have a real track record, at least not as far as is visible to end-users. FWIW Seagate does appear to be refining their SMR implementation, performace in the newest drives does look much more consistent. http://www.anandtech.com/show/10335/seagate-innov8-8tb-buspowered-external-hard-drive-review Peformance between the ST3000DM001 (7200rpm, 3.5", PMR), STDR4000100 (5400rpm, 2.5", SMR), STEA4000400 (probably identical to the STDR4000100, probably just less bundled software included as it's part of the lower-end Expansion line vs. the higher-end Backup Plus line) or whatnot, it sounds like you've already read the benchmarks. You don't need us to re-read them to you again.
http://www.storagereview.com/seagate_4tb_backup_plus_portable_drive_review http://www.anandtech.com/show/9489/seagate-backup-plus-portable-4tb-usb-30-drive-review Both are a single 2.5" 5400rpm 4TB disk, almost certainly using SMR per reviews. The links above are for the Backup Plus, but you can read the spec sheets on both at Seagate's site, and from the spec sheets they are almost certainly identical hardware inside. I'm not sure exactly what software packages are included with the Expansion drives as I have never used any of the included software with either but IIRC they are lower-end than Backup Plus drives so the software included is less comprehensive.