I think I can make it work in my space. I am going to leave enough overhang past the legs to maybe install a tail vise on the distaff end in the future, or whack a little length off and not have a tail vise.
My current bench coming out of the old more cramped shop space is all Doug Fir, 24x48 top. The old bench meets my needs in every way except it only weighs about 135#. I am sick and tired of chasing my workpieces around the shop floor. I want to hit at least 300# and don't mind going over a little bit. The one time I had a stable workpiece on the old bench, I had 135# of bench, about 50# of crap on the shelf, and 8 feet of 8x8 timber clamped down to the bench top. That piece I could work on, hard and fast, with both hands.
My tentative plan is local birch top, 8/4 by 6" nominal, with homestore DF 4x6 for the long stretchers. I have the four legs already seasoning, 4x7 nominal for the leg vise end, 4x6 nominal for the distaff end, all FOHC Doug Fir, between the 4 legs there is one knot too many to grade them select structural as a single plank. I want to find some 6x6 for the short stretchers, but I don't want to use spruce because it loses length as it seasons, and I don't want to use local birch because at that size there will inevitably be pith on center.
The main conflict for me is do I build a 6 foot top or an 8 foot top. I like being able to hook the toe of my work boot under the long stretcher to sort of clamp myself to the bench when planing long boards. I like being able to get the ball of my foot on the long stretcher and my knee under the benchtop to sort of clamp myself to the bench for little fussy things that require a moderate to large hammer. I like having having the benchtop at a comfortable working height.
I am 5' 10" and buy my clothes off the rack. With a six foot bench and my ergonomic parameters I am not confident I can hit the 300# bench mass goal. With an 8 foot bench I should have no trouble bringing it home in all four parameters.
Does anyone with an 8 foot bench, anything over 90" long really, regret building that big? The only thing I will have to change to my scale model shop layout to make this work is move the sharpening stones to where I can just turn around to use them without having to walk around the end of the bench. To reestablish a hollow grind, I will have to walk around the end of the bench to get to the grinder.
I am going to start reading up on the various US aircraft carriers. Wasp kinda sounds like a good nickname for a bench. So does Essex. I wonder if it would make someone twitch were I to carve shallow little lines in my bench top to represent steam catapults.