CTEs and re-use

I have a lovely little CTE/select doing exactly what I need it to do.
Unfortunately I need its results in the next query. I have this in the
function def below.

The gripe is that the function puts the results of the CTE/select into a
temp table for the follow-on query. That mean I have a name collision
and have to drop the temp table.

I've tried in-lining the CTE/select put the performance is horrible. (
From 10 seconds (tolerable) to over-a-minute-and-killed intolerable.
The CTE is the long pole in the tent; running it standalone takes 9.9
seconds).

What am I missing here in building the fence and losing the neighbours?

The CTE/select gives me the minimum value for all markers involved. The
second part finds the "segment" from which that lowest p-value came, per
marker. Then we reduce the list to distinct segment/p-value combinations.

create or replace function optimal_pvalue_set(people_name text,
markers_name text, chr int)
returns table (segmentid uuid, optval numeric, firstbase int) as
$$
declare
mkset uuid;
begin
select id into mkset from seg.markerset where name = markers_name and
chrom = chr;

create temp table optmarkers as
with segset as (
select s.id
, s.chrom
, s.markerset_id
, s.startbase
, s.endbase
, ((s.events_equal + s.events_greater)/(1.0 *
(s.events_less + s.events_equal + s.events_greater))) as pval
from seg.segment s
join seg.probandset i on s.probandset_id = i.id
join (select people_id, array_agg(person_id) as persons
from seg.people_member
group by people_id) as pa on i.probands <@ pa.persons
join seg.people o on pa.people_id = o.id
where
s.markerset_id = mkset
and o.name = people_name
)
select m.id as mkrid
, min(ss.pval) as optval
from segset ss
join seg.markerset_member mm on ss.markerset_id = mm.markerset_id
join seg.marker m on mm.member_id = m.id
where
m.basepos between ss.startbase and ss.endbase
and m.chrom = ss.chrom
and mm.markerset_id = mkset
group by m.id;

return query
select s.id, o.optval, min(m.basepos) as firstbase
from optmarkers o --- <<<<----------------------------Tried
in-lining the CTE here.
join seg.marker m on o.mkrid = m.id
join seg.markerset_member mm on m.id = mm.member_id
join seg.segment s on mm.markerset_id = s.markerset_id
where mm.markerset_id = mkset
and m.basepos between s.startbase and s.endbase
and ((s.events_equal + s.events_greater)/(1.0 * (s.events_less
+ s.events_equal + s.events_greater))) = o.optval
group by s.id, o.optval
order by firstbase;
end;
$$ language plpgsql;