Welcome to ECF Cradlemycoinpurse819.
I own the following...they're all fairly recent so you should have no problems obtaining them.
StattQualm SQuape Arise (MTL-DL). It's very easy to build on and has excellent flavor. It offers RDA like flavor in an RTA.
Atmizoo Tripod (MTL-DL). It's also very easy to build on and has excellent flavor.
Dvarw DL FL is really good. I was able to kill the whistle by installing one of KHW Mods optional airflow inserts. Dvarw's offer great flavor. Easy to build. I vape it from a very airy MTL to DL, depending on what AF insert I have installed.
Dvarw MTL FL is also really good. KHW has optional AF inserts for it that offer everything from a proper MTL (0.8mm AF) to a restricted DL. Out of the box it IS whisper quiet.
SvoeMesto Kayfun's, any of the current ones are excellent. I have some Prime's and KFL19's.
Hussar Project X (MTL - RDL) is great, if you can still find one. Like the Arise it offers RDA like flavor in an RTA.
I have several older HE RTA's, mostly Kayfun's, but those are not available anymore. You can still find them on the resale market from time to time. Also once in a while in our classifieds.
Hope that helps!
Did you ever sell your Hussar Legacy X ??? Please let me know. TIA
ETA: I don't have a GT4 so I can't say if those ^^^ are on par or not.