Unless you have an incredibly weak achilles, are doing way too intense training or are very unlucky, I'd say you don't have to worry about a rupture, it's a fairly extreme injury.
The stretching is essential, as is not doing any explosive or fast running without a good warm up. That's why we always include the 2-3mile easy pace warm up before your 1 quality session.
As a rule of thumb is something hurts or aches to walk, don't run.
Backing off and stretching a lot, got me through achilles tendonitis myself. Very key for you to monitor though...
In an ideal training plan, you'd have your tempo session a week, as you've been doing, and also a speed reps session. In your circumstances, you don't have enough mileage to play with to add a second quality session.
However, i think we can acheive that syub 1hr 35 goal from the weekly tempo and long run. Those are key.
Your old paces got you used to working too hard each run, meaning you were never fresh, probably a reason why the achilles is sore these days.
I'd envisage that that will start to ease down, and the new plan will work you out at the right levels, yet also keep you fresh to improve.
Edited: 30/07/2012 at 11:52