Using serial port with VMware Player

I've some reliability problems with serial port with VMware Player (on Windows system)

I must say that the application in virtual machine using serial port in very huge load because it communicates with PLC device every 100-200 milliseconds.

In this scenario, what are your suggestions about my questions:

1. It's better using physical RS232 card port or USB-RS232 converter ?
2. If i'm using USB-RS232 converter, it's better connect it to host machine (and then mapping) or connect it on virtual machine ?
3. Are there some settings to increase reliability ?
4. It's better using workstation instead player in this case ?
5. Do you have physical RS232 card port or USB-RS232 converter 100% reliable to suggest me ?

Thanks for support,
Rinaldo