TT or no TT?

Over the off season, my "training" consisted primarily of changing my diet to more healthy foods.  As a result, I've lost about 22 pounds and I'm still losing weight regularly.  Not complaining, of course, but my times, especially for running, but also in the bike and swim, are heading downward much faster than ever before. As a result, my "normal" time goals I've used over the last two seasons for races have lost much of their meaning. I'm in uncharted territory.

Last season I had LT tests done for both bike and run and trained according to the zones established by those tests.  But now I'm finding that, with the weight loss and better nutrition, those zones seem to have shifted upward by at least 5-6 bpm.  I seem to have lots more energy and can perform at a much faster pace for much longer than before.  As a result, I no longer know what times to expect in my training.  The obvious solution is to have another LT test done, but right now my weight is still going down so I wanted to get near my optimal weight before spending the money on a new LT test.

Plus, I have my first sprint of the year coming up in several weeks and I'm totally clueless how I should expect to perform.  It's a reverse with the run first.  Several of my regular tempo runs have been (for me) ridiculously fast (roughly a minute per mile faster than last year's race PR).  My concern is that because it's a reverse tri I have to make sure I have something left after the run.  At the same time, I'd like to take full advantage of the situation if I can.  So I'm wondering whether I should do a TT at race distance a couple of weeks before the sprint in order to establish a baseline and then plan my race goals based on that.  Or should I just go and race, have fun, let the chips fall where they may, and use that race performance as the baseline for training until I can get re-tested?  I'm confused and just a little nervous going into a race with no clear idea of how I should perform or what I'm capable of.

Any thoughts or suggestions would be appreciated.