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Yeah, its the 152 cft x 2 that makes all the difference. 300cft in a single cylinder is another story (usually in the "I want to see a tank explode" thread).
I think your poll is going to be a bit limited in choices for most people. I have LP108's that I bought for cave diving. When "cave filled" they hold ~300 cft of gas and I found them to have comfortable trade off of weight out of the water and buoyancy characteristics in the water.
Sorry, I thought it was obvious I meant doubles.