Save your money and get those limiteds
If you are already comfortable with primes, you'd unlikely need to use zooms. I too have primes and some zooms, but the times I use the zooms is only out of necessity to give them some 'exercise' (get the moving parts moving)
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If you really want to try zooms out.
The DA18-135 impressed me with its WR, small package for so much focal length coverage and very good close focusing ability (40cm at 135mm FL) which is very useful for a all round walk around lens.
Don't have a 17-50/2.8, but my 28-75/2.8 is great for its general utility while having the fast aperture for low light and shallow DOF shots. Pity its no wider than 28mm though. I'd guess the 17-50/2.8 is about the same except that its wider on the wide end, but a bit short at the long end for some portraits or reach.