MechengPhoenix - 2012-02-04 1:02 PM I came up with a simple model.
Assume your choices are narrowed down to Clincher1 & Tubular1. Assume also that there is no difference in aerodynamics between the two. There might be a slight difference in Crr that you may be able to find for many tires here. An analytic cycling calculator will be able to estimate the time difference between the two over a hypothetical course (flat windless 40km for example).
Let T1 be your elapsed time over the course using clinchers, & T2 be the elapsed time for tubulars. Denote the probability of getting a flat using clinchers as P1. Under racing conditions you can change it in time F1. Likewise P2 & F2 for tubulars.
The difference is then D = (T1 - T2) + (P1*F1 - P2*F2). If D < 0, go with clinchers. It is up to you to figure out how fast you can change each, as well as the probability of getting a flat based on a myriad of inputs (user reviews, miles on tire, course quality, etc etc).
Like I said - it's a simple model. It doesn't account for multiple flats or the difference in Crr after changing a flat (for ex. flatting on latex & replacing with a butyl spare).
Edit: replaced broken link - seems like biketechreview is DOA