tial used to serve 35, 40 and 46 gates
they have since changes their line to 38, 44 and 48 i think it it is.. im not sure.
but basically, the 38 is a 2-bolt flange, and the 40 is a 4-bolt flange.
Now, spring pressure doesn't have much to do with the physical size of the unit. If you have more gases to bleed off (like most hondas do, running a big turbo running moderate boost) the larger gate will allow them to escape faster avoiding the chance of spikes.
small turbos running big boost (like a dsm) don't need as big of a waste gate, as theres less to bleed off.