This maybe a stupid question, but I will ask it anyways. I just flatted my rear wheel which had a TUFO Carbon Composite
tubular. This TUFO set had less than 500 miles on it. The front tire still looks brand new. I bought a set of Bontrager X-Lites and
replaced the rear flat, but I am debating on whether or not to leave the TUFO on the Front and use it until I am forced
to replace it. I also have older tubes that I can use as a spare that have some wear, but will definitely get me by if I flat
in a race. Do I put the other X-Lite on the front so the set will match and use the TUFO as a really nice spare, or just leave
the TUFO on the front and save the other X-Lite for when I really need it?
I would wait until you needed to replace it …even though you are committing an ST cosmetic faux pas 
.
Fine to do - forget the fashion police. However, I would “review” the many rolling resistance/speed tests for tubular tires prior to my next tubular tire purchase! You have cost yourself a good 10 watts with your tire selection(s)
I know. I saw the list that Jens posted and the Tufo Carbon Composites were dead last. I don’t remember seeing
the Bontragers on the list, so I’m not sure if that is a good or bad thing. I really didn’t have much choice since
that is all my LBS had in stock, and I couldn’t afford to miss any rides with Lifetime next Saturday.
Yeah, I was running Conti Sprinters for a while and finally replaced them even though they really weren’t in that bad shape (takes a while, even with IM to kill a race only tubular!). They don’t test very well either, but were comfy and relative flat resistant (of course, I flatted at IM FL on them!)
I don’t think you have to go with the absolute best tire tested as there are so may variables (age of the tire, kind/age/type of glue job, etc.). Latest tests are trying to show these variables now. A good, high thread count, latex tubular is all you need. I ended up going with some Veloflex Carbons (instead of the faster, but thinner Records) as they test VERY well, still 22 mm wide, and ride nice (important for long events). If I were simply a TT rider, I’d go with the Veloflex Records (BTW, the Veloflex guys are the previous Italian handmaker of tires that stayed in Italy to form Veloflex from Vitorria when they switched production to Taiwan). I can honestly tell a slight difference on my WAY less than scientific trials. “Tests” say I should have gained about 8.5 watts per wheel and if correct, I’m sure one could “feel” (or at least by the clock) 17 watts.