FWIW- I shoot a similar set up, draw length around an actual 27" similar poundage and I found that a .500 spine 510gr. arrow shoots really well from my bow. I'm actually going to try some aluminum 2117's just out of curiousity to see how they shoot. I believe the actual spine for a 2117 is .400 but I have an assortment of heavier tips to try so I can actually tune the arrow.
That's what I would suggest is tuning with the proper wt. point. Keep trying different weight points until you find the one that shoots the best, and I would also recommend that you don't cut your arrows all the way down until you get them tuned. Once you cut some off, you can't put it back on. If you work down in 1/4" or 1/2" increments a little at a time you may find that a 29" shoots better or shoots just fine and no need to cut them all the way down to a 28" ??
These aluminums that I'm going to try are a full 31" and I'm not cutting any of them off until I see if it's completely necessary.