Hello kenniepark. I've been busy so my apologies for not answering your inbox inquiry right away. I think you are going to have a typical task - at the moment - finding anyone who owns the quad and other customs to compare it to. Unfortunately (and fortunately) the 1964-Q is the only custom I own at present. I will purchase some other customs down the road, but money won't allow that right now. So, I have nothing else to compare it to other than the universals I have heard. My thoughts about the quad and the universals still stand - no universal I've heard really comes close to the sound of the 1964-Q.
Now, the only person I know of who owns the quad and other customs is jermng, but I haven't seen him on head-fi in some time. You might want to inbox him and ask him his impressions (he owns the quad and the ES5 I believe, and maybe one other custom). Sorry I can't be of more help to you at the moment. Happy listening.