I owned a Schecter Stiletto Deluxe (no longer being made from my understanding, now the Extreme is on the low end of the totem pole- however both deluxe and extreme were identical, just aesthetic differences). I've owned a few other Schecter basses including the Schecter Stiletto Elite - Nice basses for sure for the money. The Extreme (I did try However, much like you, I've heard so many good things being said about Sire too..so much so I bought one today. A Sire V3. Going on a leap of faith here, but everything I've seen, read and heard about Sire basses make it a risk worth taking. I guess i"ll find out for myself soon enough. No music store anywhere near me has one, so we'll see.
However, here's a few main things to consider....the Sire M2 has a 3 band EQ, and an active/passive switch. The Extreme is 2 band EQ, no such switch - when I owned my Stiletto basses (Deluxe and Elite), my main beef with them was the 2 band EQ, and need for more mid control- you get that with the Sire.