Unfortunately this applies to many male airsofters too... yes I'm in that category.
I wanted a mk4 in my collection & got one to wear in game too... damn thing weighs a tonne.
Out of the gear I have, the best/comfiest is an old DPM chest rig, the most uncomfortable is this UCP TAP vest( the layout is fine but the drag handle digs into the back of my neck due to ALL the weight being at the front, the DPM one is a better design but not adaptable with molle.
As above there are much better/tacticool chest rigs on the market, have you tried a belt kit/webbing?