Question swapping cpu trays

Im new to the mac pros but so far so good, came from a imac but liked the way you can customize these its more my style.

I have 2 mac pros right now and will only be keeping one

first one is Mac pro 5,1
Processor Name: Quad-Core Intel Xeon
Processor Speed: 2.8 GHz
Number Of Processors: 1
Total Number Of Cores: 4
L2 Cache (per core): 256 KB
L3 Cache: 8 MB
Memory: 8 GB

this one has built in wireless 8gb ram and the radeon 5770 and a 1tb hard drive

my other mac pro is a model 4,1

Two 2.26GHz Quad-Core Intel Xeon "Nehalem" processors
6GB (6x1GB) of 1066MHz DDR3 ECC memory
640GB Serial ATA 3Gb/s 7200 rpm
18x SuperDrive (DVD±R DL/DVD±RW/CD-RW)
NVIDIA GeForce GT 120 with 512MB GDDR3 memory

this one has no wifi, smaller harddrive, weaker video card but I want the 8 core so i took out the tray at the bottom with the 8 core and put it in my 5,1 which had the 4 core and it booted up fine except all the fans started blowing full blast and got real loud I got kind of scared and turned it off.. I could also just probably swap the hd, video card and airport card over to the one with the 8 core but the 4 core case is nicer condition, anyway any help would be greatly appreciated and hope I didnt confuse anyone thanks