Dell R440 CPU UPGRADE

i Have 3 R440 Server

1. BASEBOARD : XP8V5 ASSY,CRD,PLN, R540/R440,MLK V1 - default cpu Xeon 4208

2. BASEBOARD : 8CYF7 Assembly,Card,Planar,R540/R440,V2  - default cpu Xeon 4208

3. BASEBOARD : 4JN2K ASSY,CRD,PLN,R540/R440,MLK,V2 -  default cpu Xeon 4208

each server have 2 x 550W PSU
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i buy  a Xeon 6240  , and remove default cpu . put Xeon 6240 but cannot boot
got error  UEFI0384 Unsupported processor.​

but in this forum there a thread says to put on BASEBOARD : 4JN2K, this will try tomorrow

Thermal restriction matrix says ok .
question is. if i cannot use that proc. what the correct CPU that have a lot of core , that i can use on  Server 1 and server 2

hope somebody can share their experince here..

Thanks.