Imperial plate bonus?

[Ubrpwnage2]

Does anybody know how much Str the 4 piece Imperial plate set gives? Would it be worth it for a ret?

 

[Tobz.eu]

13 Strength - but I'm not sure 4 items are available at level 49. Might be wrong

 

[StS Ralso]

only 3 items usable at 49
https://www.wowhead.com/item-set=321/imperial-plate