The real problem is that you can know the frame tubing material and still not know anything about the tubing "design", i.e. wall thicknesses and butting and the resultant weights. Higher strength steels like the TT OX you mention ALLOW the use of lighter gauge tubes, but don't necessarily mean that is what is going on. Having said that, it is USUALLY true that premium materials are used for a purpose, e.g. when the object is weight reduction and more compliant ride. You just can't be sure what the actual final product is like by knowing the steel used to build the frame. What can be said is that 4130 is basic chrome-moly steel, stronger than so-called high tension steel and tolerant of a lighter build. If, as mentioned by another poster, the OX is heat treated chrome-moly (maybe heat treated 4130), that means it is stronger yet, and therefore, tolerant of an even lighter design and build. To answer your direct question, the TT OX SHOULD be lighter than the basic 4130 frame, because it can be and why use if for any other reason. You just never know, however.