Saltine,
First, welcome to the AT forums.
Second, wise not to rely on ANYthing TigerDirect and subsidiaries have to say. The 3870X2 is nowhere near 13" long - maybe up to 11" like the other long cards. In any case, the extra room of an EATX tower is welcome.
None of the ones mentioned above are really set up for cards longer than 10 or 11 inches as they only support standard ATX length mobos - I have one of the Masstige series Aerocools here (silver CoolView) so I'm sure on that one - it is also for sale. However, if you keep your drives out of its path, the card would likely fit in the Masstige series (inverted Stacker type cases).
. Depending on where you live, the Rocketfish Full Tower can be had from BestBuy (check the web site for availability at your local stores and then call to find your best price - low prices are in-store only) for $120. or lower. If you can't find at any at your local stores, I have a couple for sale in my For Sale/Trade listing (linked below) - but not as cheaply as at some local stores. I have been told that the RFFT was originally priced at $299. - I doubt it, but it is basically an all-aluminum Lian Li.
. Any case that can take an Extended ATX (EATX) mobo (like the RFFT), can handle that card easily: Silverstone Kublai KL03, XClio WT (WindTunnel)/Tagan Monolith (both are the same case), Enermax Uber Chakra, Gigabyte Aurora 3D 570, Chenbro SR10568/69, Ultra m998 (may have to relocate the power strip), Cooler Master Stackers, etc. etc... Unfortunately you can't just enter "Extended ATX" or EATX in the search field at Newegg or Directron and have ALL the EATX-capable cases they have pop up. It will require several searches on various attributes like 13 or 13" (length of mobo accommodated) to find them all. The egg is way more inconsistent in its product descriptions than most - hard to find all in ANY category w/o several searches and the descriptions often lack essential info like dimensions of cases...
Re. obstruction of SATA ports. There are some SATA cables with very low-pro right angle connectors - the OK Gear ones I've got have only a 5/8" rise, but they only have the right angle bend (plugged on a HDD, the bend is down - on mobo connectors, bend is toward bottom of case assuming normal mounting in tower case), satacables.com also have "left" angle (on a HDD, the bend is up). So one or the other may be used to avoid blocking the neighboring SATA connectors. I don't think the "left" angle ones from satacables are quite as low-pro as the OK gear cables.
.bh.