I did exactly that. Kept the M87 for a year just in case, then sold it. The Cali is, IMHO quicker to react. Apart from that, to my ears the M87 will stay very transparent but add a certain strained fartyness to the tone when you redline it. The Cali gives you rounded edges and a certain warmth when it engages. I was looking for a transparent comp but wanted to own a Cali for about a decade now so I bought one on a whim when a good offer appeared for a second hand unit - along with a Keeley Bassist. I was pretty sure that the Bassist would become my new comp, but with the Cali, it was an instant love affair.