I would go with the 2" Blazers if you are using mechanicals. The weigh roughly 5.5-5.8 grains a piece. They are listed at 5 grains each but I have weighed several and never got one under 5.5. I have shot 3 Blazers on my arrows with mechanical heads with much success. I am fletching some arrows with 4 Blazers this year and they seem to control the arrows just a tad bit better. They might fly better through a WB than longer vanes.

My old Buckmaster G2 had an IBO rating of 309. I was shooting 383 grain arrows at 268fps so you should be close to that.