Thin race tires are fun to ride and save a few watts of rolling resistance. Not inexpensive or terribly practical, due to the short wear life and tendency to puncture or cut through, but fun. The last ones I tried, Open Corsa CX, rode great but punctured and cut easily and didn't last more than 1500-1800 miles on the rear (I buy in sets of 3). For me, the GP4000 has provided the best compromise of long-life, smooth ride and roadholding.
Would be interesting to hear your comments about the Panaracers. Suggest you stay away from 150 psi though. That extreme max rating may look impressive on the sidewall, but it's no good for the real world. First, most rims are only rated for 140 psi. Second, tires inflated to rock-hard transmit every road imperfection through the bike to your body, resulting in no advantage in rolling resistance except on a glass-smooth track surface. Third, ride, handling and road grip are destroyed at ultra-high pressures. On a fast bumpy descent, stability and roadholding are the priority. A bike that holds the road and steers well allows confident, fast decending. Lastly, high pressures reduce puncture and cut resistance. IIRC, Conti rates their tire's puncture resistance at 95 psi. I like to use 100 front, 110 psi rear.
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