The 130 weighs 43lbs
The 121 weights 49.9lbs .... so not any lighter
The 130 has 9.7lbs buoyancy shift
The 121 has 9.1lbs buoyancy shift ..... not what I would call significantly better
I have dove many times with a 121, that is a frickin long tank. I mean ya I am really short but even on guys under 6' it is not the easiest to handle. Especially if you only have 1 camband, then the tank likes to pull and "roll" you over in the water. Yes you eventually get used to it but it takes a while.
To decide on a tank you have to decide what is most important to you. Is it cubic feet, length of tank, weight of tank, how about efficiency of tank weight (ie lowest pounds per cubic feet), buoyancy shift (must it remain neutral or negative?), will you be going to doubles later and want one that is easy to double up etc...
So take your time and figure out what is really important to you. Because what you need today might not be what you need in a year or two. I made my decision based on length of a tank and cubic feet, because I need the extra air for deep dives and I am not going to get any taller. Good luck!
Maybe there are some weight differences between brands of LP 120's..... I have a couple of HP 100 steels, that are ridiculously heavier in the water, than my OMS lp 120... The Hp100's are ok for my dry suit, but in summer, if I try to use them with an 18pound lift Halcyon wing, it takes the entire 18 pound lift of the wing to get me neutral ( also wearing a light cannister--this is only other wieight beyond steel BP).
With the lp 120, it takes about half of my lift potential in the 18 pound wing...still not good, but feasible if needed....
My solution was to start using a Halcyon 30 pound wing witht he 120's, and only use the 18 pound wing in the winter, with a drysuit.
But I like that I "can" use the lp 120 with either wing, and don't have to use a drysuit with it...
As usual, TS&M is right....for the use in the colder waters the poster has, as long as he is always in a drysuit, the 130 may be just the ticket....I don't think it would be good with a thick wetsuit--it would be at least as lame as my hp100's would be--causing the diver to be extremely heavy if they hit 120 feet for more--possibly dangerously heavy. Then again, some divers will never want to dive deeper than 60 feet, so for them, this may not be much of a problem.
But I expect others here will agree the 80 cu ft tank for nitrox and deeper than 75 feet, is a mistake everyone needs to fix