Lanovran

The biggest difference between the 7.5 and 7.6 are in the drivetrain and shifter setup: i.e., 9-speed vs. 10-speed cassette, with upgraded shifters (Sora & Deore to some nicer SRAM stuff). This gives you a setup with greater low-end "climbing" gearing. Other differences in the 7.6 include the lighter weight seatpost and stem, and better quality brakes (calipers and levers both). The 7.6 also comes stock with 700x25 tires instead of the 7.5's 700x28s, theoretically meaning less weight and rolling resistance on the 7.6. Basically, the 7.6 is as good as it gets in the FX line without hopping up to the full carbon 7.7. It has the same frame and wheels as the 7.5, so that price difference is all in the componentry upgrades. If those are significant enough for you to invest a bit more in the bike, then go for it; but if not, then no worries.

As for the pricing, that will vary between dealers. Typically, the prices are set by Trek, but more often than not, dealers have some leeway in how they price their bikes. That being said, I certainly can't speak towards what other dealers are going to do with their pricing and/or sales. I can tell you that the regular advertised prices for those bikes are $1099.99 and $1319.99, respectively, so the prices you've mentioned are at an 18% discount for the 7.5 or a 20% discount for the 7.6. You've apparently got the option of the 7.6 at less than the regular price of the 7.5, which is not too shabby. Ultimately, it's up to you to decide if it's worth the extra amount.