Most or all of the people who don't like the green 150kPa caps, and run lower pressure caps on their cars use the 75kPa black caps. It would seem to me that that just going down just to the white, 100kPa caps would give the benefit of lower pressure, but without lowering it all the way in half. This would still reduce the stress on the cooling system by a considerable amount, and maintain better protection against nucleate or localized boiling than the 75kPa caps.

Or is there a reason that I don't know about to avoid the white, 100kPa caps? And, a priori, the white, 100kPa caps are still available from several sources (including the Volvo dealer, for a whopping $56 plus tax), so that is not it.
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Scott Cook - 1991 745T, 1985 RX-7 GSL-SE, 1986 Toyota Tercel (Don't laugh, it is reliable, faithful AND gets 41 mpg!)