I calculated the seats for my hypothetical proportional representation California Senate by comparing the results of the 2002 and 2003 gubernatorial elections. Since they were so close together it's reasonable to assume that the different results were because of the systems, not because lots of people had changed their views.
The 2002 results were:
Democrats (Davis) 47.4%
Republicans (Simon) 42.4%
Green (Camejo) 5.3%
Libertarian (Copeland) 2.1%
American Independent (Gulke) 1.7%
Natural Law (Adam) 1.1%
The top finishers in 2003 were:
Moderates (Schwarzenegger) 48.6%
Left-wing Democrats (Bustamante) 31.5%
Right-wing Republicans (McClintock) 13.5%
Green (Camejo) 2.8%
The 2003 votes for Bustamante and McClintock give us the %ages for the Left-wing Democrats and Right-wing Republicans. Those combine with the moderate wing of each party to give the 2002 %ages for Davis and Simon. The minor parties can keep their 2002 votes. The 40 senate seats would be allocated at one for each 2.5% of the vote, with the left over seats going to the parties with the largest remainders.
This is a rough approximation. Don't take it too seriously. In particular, the relative proportions of moderates in the Dems and Reps are probably distorted by the Dems wanting to protect their incumbency and the Reps wanting to back a winner. Suggestions for better data sources will be eagerly accepted. Comparing the 2002 and 2003 elections in just percentages is also distorting, since 2003 had a much bigger turnout.