[Sprint Samsung Galaxy S III] DroidGnome:
You can use an app called FolderSync to sync your SD card just about anywhere. It's not a cable sync, so it will be slower, but you can have it scheduled to sync to the cloud, or even a windows sharepoint on your own wifi network. I use it myself to sync my SD card to my home PC sharepoint (which is then backed up to a dropbox account via the PC).

It currently supports SkyDrive, Dropbox, SugarSync, Ubuntu One, Box.net, LiveDrive, HiDrive, Google Drive, Google Docs, NetDocuments, Amazon S3, FTP, FTPS, SFTP, WebDAV or windows share (Samba/CIFS)

As for the wireless speed.. I never owned a 3D, just the original Evo 4G, and my wireless speeds are exactly the same , nice and fast on my home network. On other networks it will vary greatly as every network/router can be configured differently. I don't remember the exact numbers but my Evo 4G and my S3 had almost the same speed using speedtest on my WiFi at home.

3G still sucks, but that's a sprint issue rather than a phone specific one in my area.

As for the USB Mass Storage, no clue what you're talking about.. my S3 supports USB Mass Storage host mode just fine.. plug in any flash drive to the micro sd port (via adapter of course) and it reads as if it were just another file location. Works great.

Finally Link2SD... I'm not entirely sure WHY you'd want to use it on an S3, that app was designed originally to move apps from an internal data storage partition to the SD card. The S3 and newer devices already have an internal data space labeled 'sd_card' and have that functionality already built into the OS to use that 'sd_card' just like the original Link2SD. By that, I mean it no longer uses the 'limited' ROM storage space.

Sure you could use Link2SD to ignore the internal data partition and use a true SD card, but the access speed even with a class 10 card is going to be much slower. If you're worried about 'breaking' your phone and losing all your data (thus the reason you're putting it on SD to begin with I presume), there are better solutions.

For example, Titanium Backup scheduled to backup to the SD.. Or even to the internal then use FolderSync to transfer that backup off the phone entirely (which is what I do actually).

I used to be a HUGE supporter of SD card hacks and Link2SD on my Evo.. hell I even formatted the internal data storage to custom partition sizing to get all my apps to work. However on the S3 I've come to realize 2 things:

1) The increased internal SD space means I don't need to move apps to the external SD card at all. (I have the 32gig S3 with over 12 gigs free and amost 200 user apps (reported by Titanium). Plenty of space :)

2) With USB Host mode, I no longer need to swap out the SD card for things like my TV shows/Movies (which I put on SD when I travel) I can put them on any flash drive, then just plug it into the bottom of the phone for full access.

My ONLY complaints so far with my S3 are all touchwiz vs Sense based. Namely the contact management. (Though I like S3's calendar better, so it's a tradeoff i guess).

I even found a ROM the other day with as many customization options as MikG used to have and am loving it. (Rom is the FreeGS3 ROM found here on XDA for those interested... but Blazer is nice too just less customizations).