Leben CS-600 Plate Voltage

I recently ordered a quad of Tung-Sol 5881 reissue tubes for my Leben CS-600. The Tung-Sol 5881, which is a 6L6 variant, is a 23 watt tube and is rated for a maximum plate voltage of 400Vdc. The CS-600 has plate voltage settings for 6L6 and EL34 tubes. Because the 5881 output is more similar to an EL34 than a 6L6, does that suggest the EL34 plate voltage setting should be used? Any idea what the potential downside is of using the wrong setting?