gamma SV is much thicker and heavier material than gamma MX. both are Malden Powershield but the Mx is "Powershield Lite" which is much thinner fleecy material on the inner
SV is warmth wise, like schoeller over 200 fleece in one piece, maybe a bit heavier but more breathable than the combo of the 2. MX is like schoeller over underwear... in terms of thickness and weight.
SV fabric must weigh at least 50% more thanMX ( i say that not looking at the catalog). i would guess overall (including zippers etc) the MX is 25%-30% lighter than the SV. also less warm so more 3-season versatility. SV is really a winter thing only. too hot to wear climbing at smoke bluffs on sunny day in february.
gamma LT is just a schoeller dynamic, no fleece.
MEC has the Pamir, which is more or less equivalent to the SV bib/jacket. they also have an even thicker, heavier line called the Composite, which has thicker fleece on the inside. serious winter use only i guess.