go4broke44 said:4x6?!?! holy cow!! You might as well just dig a hole under your tank and call it a bomb shelter, haha.
Yeah, it's very over built but with a tank that weighs about 2 tons you can't be too careful IMO.
I like your revised plan. And as ScooterNH suggested, anchoring to the wall with that tank is a good idea. I saw that tank set up at Dong's(very cool tank BTW) and it looked very top heavy.
I've built several tank stands and IMO, 2x4's will be fine. No worries.