As Aeolian said;
+1 on the Sensaphonics - The ambient external noise cut is 37db. I've used Vic Firth earphones for quite some time, and the cut on ambient external noise is 28db tops. Another thing to consider is whether or not you sing back up and whether or not you play and are very animated facially. Singing and the like move your jaw, which results in minute changes in your ear canal structure. This is the primary reason why I decided to go with Silicone IEM's. Also, if you get IEMs, make sure you get a pair with Field Replaceable Wires.
Below is a rundown on the process to get fitted and have them built.
After quite a bit of research I decided to go with Silicone rather than the Acrylic. I chose to go with the folks from Sensaphonics rather than ACS for this first pair.
Went to an audiologist from Sensaphonics Certified Audiology Network and was really pleased to meet and work with him. After he completed my ear molds, we spoke for a few moments and I decided that I would come back in an hour when he had a free appt, and have my hearing checked. I wanted to get a baseline for where my hearing was prior to getting into the IEMs. I should note that I have made a commitment to my hearing and have protected it where possible. That said, when I was in the Mil in the early 80s, we did not use hearing protection on the range or any other time. I've also been to concerts sitting in the 8th row, and had ringing in my ears for 2 days after that. I communicated all this to the audiologist after the test. When I came out he said that I should be a spy, as my hearing is outstanding. I shared the ear damaging stories with him and he indicated that those events must not have crossed my permanent damage threshold. I was surprised.
Sent in the molds on Mon 9/16 and received my 2X-S IEMs 9-27. They built them in under a week. The organization provided outstanding comms and was quick to return my call & email. Upon receipt and checking them out, I am thrilled as they cut ambient external sound by far more than 28db (like my Vic Firth isolation headphones). Indications are that the ambient external noise cut is in the 37db range; Holy Cow!! When you wear them you can understand why some musician's don't like them as they make even normal speaking difficult unless you read lips. I can understand how in a performing environment with the crowd noise, would make speaking with people (with these IEMs in), next to impossible. I'm OK with the trade off. My hearing is worth it. Prior to these IEMs I performed with ear plugs in my ears and a JBL wedge to my left over my shoulder. I still use the wedge, but just for the bass 'feel' it gives me.