add more RAM ?

2 old mac pros,

mid 2010

2.8 GHz Quad-Core Intel Xeon

one with 16 gb ram, = 4 x 4gb sticks

other with 24 gb ram = 3 x 8 gb sticks [they are a heavy photoshop user

both mac pros have 2 mechanical HDs in them -

boot drive is fast 1 tb, 'clone' drive is also  1tb but slower  and is only there for clone and emergency purposes

recently upgraded to 10.11.6

and

adobe cc 2017, idd, illus, photoshop

customer kept adobe cc 2015 add, illlus, photoshop on both mac pros

talked to customer and they said they keep all 3 apps open at a time but do not mix 2015 and 2017

to give them better performance at a good price, i was going to upgrade

24 gb mac pro to 3 x 16gb =  48gb ram

and then take that ram and put it into other mac pro

3 x 8g  = 24 + 1 x 4 gb = 28 gb

apple had suggested that 3 sticks of ram is better than 4 sticks of ram

any suggestions would be helpful

ps - i have talked to client about SSD drive but 1 tb SSD is expensive and then there is cost of sled

what is nice about ram solution above i that only ram is re-used to keep cost of solution low

thanx !

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