I shoot a longbow at 56# & my 2016's are 27 1/2" with a 145grn woodsman head. These shafts & head combo took a bit of tuning but fly like darts at this poundage & arrow length.
I tried 2018's as well but they were way too stiff until I loaded the front up with 200grn, once I did this they planed out beautifully. Before that they fishtailed uncontrollably.
The thread starter shoots a 53# bow, I assume he has a 28" draw since his arrow length is 29"---if this is so a 2018 will most likely be too stiff for his description, I hope he will at least give the 2016 a chance, if he were shooting carbons he would only need a .500 spine shaft, after all he's only shooting a 125grn head.
Like many here I play with a whole lot of arrows & setups to achieve what works with which bow & draw weights, I feel the 2016 will fit the bill over the 2018. (grin)
ElkNut1