I did this mod today on a R33 S2 Auto. When I first read this thread I was a bit skeptical about the results, however, I must admit that it has made a huge difference. Although, I don't think it was all due to the larger SMIC 'cause the original was in pretty poor condition (had a leak) and I also found some of the hose clamps on the pressure side of things were a bit loose.
I must say that the turbo seems to spool up a bit quicker now and it also sounds alot better with the boost coming on earlier than it was and my 'seat of the pants dyno' tells me I've gained an extra 20 or so KW.
So to summarise...............I'm very happy that I did this
By the way. I'm also running a full 3" exhaust and MBC set to ~10PSI but still have the standard air box.