Slow performance

[Anadrol]

Hi folks,
So, I have been trying to find a solution for that issue.
I have the following setup

VMWare ESxi deployed on Dell 720
Theis Dell is having 4×1Gig interfaces bundled to a Cisco 3750 switch.
Inside the esxi, I have one debian machine running openvpn server as well as NAT (to provide access to VPN clients)

I have external machine connected to the same Cisco switch
Did the following testing

Speedtest application from the vpnserver , get sold 900 Mbps.
Speediest application from the external machine get solid 900Mbps.

I point the external machine to the VPN server ( as a gateway only) get solde 900 Mbps

I connect a machine via openvpn connection (VPN enabled), Speediest gets 30 Mbps

Tried all sort of tuning mentioned online
Tun-mtu / mssfix / disabled tcp segmentation offload/ changing kernel tcp remember and wmem values

Nothing is working, any advice?