I know that there are similar questions here, but I still don't understand everything. I wrote 4 almost identical sentences below with a place for an article marked as "...". Please tell me what are correct articles here. I know that these sentences can be rewritten without articles and with keeping the same sense, but I am interested in these particular examples. It is not a homework or something like that by the way.
We must keep it at ... higher angle.
We must keep it at ... high angle.
You must drive at ... high speed.
You must drive at ... higher speed.