I bought the XL in 174 after demoing it in 184 and 174 this season. I am 6'-3", 205lbs, level 7-8 skier, 20 days per year. At 184 you are looking at a GS ski that is very fast but short turns are work while at 174 you can make shorter turns w/o wearing yourself out and the 174 is certainly better in the bumps [this was initially an important factor for me]. The trade offs are a little loss in stability at high speeds [not much], plus less float in powder.
After 5 days on the 174's this season, mostly in powder and crud conditions, the lack of float at my size and the decrease in stability in crud became an issue [during my 2 days of demo of the XL I was unable to find any powder or crud- naturally!]. As a result, I elected to purchase the ski in 184 and will be selling the 174's next winter [missed the window to sell this year].
Interestly, the 184 XL's I bought slightly used had the bindings mounted a little more forward than the 184 XL demo ski. The difference in the mounting I thought was significant in terms of control and feel. Carving a bunch of short turns on the 184's is still work, but easier now, plus I am better balanced over the ski in general, and, the additional float and stability in crud with the longer skis is much better.
If I were mostly looking to ski groomers with shorter turns, as well as, bumps, I would still be on the 174s FWIW.