Greetings, and welcome!
Typing this from an ECS 755-A2 running Linux. The system is loaded, with AGP card, dual channel SCSI and TV card, four SCSI and two IDE drives, internal USB card reader and the usual bunch of external peripherals. Also, this is my test rack for any kind of hardware passing through, so it's seen a lot more hard disks, processors and graphics cards than what's in there now. No hiccups ever. I'd buy another any day.
Incidentally, this is also the cheapest S754 board out there.
If your 3400+ is an Athlon-64, just go ahead, mind power supply strength. If you plan on a Sempron 3400+, you're going to need a board from a very recent production run - for no other reason than getting a BIOS that runs this very latest CPU stepping. (The board does run them - I've just last week downgraded mine from an Athlon64-2800 to a Sempron64-2600.)