Excerpt from Jennings on rotary disc-valve intake opening:
"If there is a rule, it is that the point of opening for rotary valves is best established right at the point of transfer-closing if you want a very broad range of power. On the other hand, maximum power is obtained by opening the intake port somewhat earlier: from 130- to 145- degrees before top center, which means that the intake and transfer ports have overlapping open periods. This presupposes that the engine will have been fitted with a proper expansion chamber."
He expands on this, so don't just cut to the max and hope it works, but it seems one can get a bit more aggressive than the anticipato cranks, by about 10° on each side in a stock case with a maxed out intake, especially on a variated engine where You don't really care about the low end.
A bit less in the polini speed case, as it gets you 6-10° more duration that's about 5-8° advanced compared to a modified stock intake. It actually closes earlier (http://vespa-ciao.nl/page.php?id=180) so there'd be more room on that side, but the opening would already be in the mid 140s. (edited)