I can't tell for sure from your photo, but is that a borer hole in the middle of the cut end of the dead cane portion in question? If it is, removing the damaged section to live, good growth will produce and expose a fresh cut that will be vulnerable to future borer damage that will need to be addressed. Most folks who have borer problems seal fresh cut ends to prevent new borer invasions. If the dead section is due to borer damage, the soon to emerge insect may still be in the stem or it may be old borer damage and the resident insect is long gone. The stem will continue to die down to the point where the insect's tunnel terminates. Some borer tunnels go down as far as the crown! Everything has to be cut back to tunnel free good wood then the cut end sealed. If that dark spot in the photo is not a borer hole, I do what Marlorena does, cut back by increments to good, white pith wood. All growth above that point is sacrificed.

It did hurt a little chopping away at green, sprouting canes, but what nanadoll and mad-gallica said about the twiggy, spindly stuff made sense. Next year, I'll probably trim a week or two earlier, before the roses have a chance to put too much energy into new growth that will get cut off anyway.

Olivia can get up to 6+ feet in 2-3 years in California and elsewhere with mild winter. Unlike in the UK, it is definietely not a rose that stays within the 4 feet tall range. In fact most David Austin roses that said 4 feet in height in their catelog will get to at least 5 - 6 feet unless you live in areas with issues of winter die back, in zone 5 - 6. My Olivia got up to 6 feet after 2 years even with extensive summer pruning. It does throw octopus canes. During its first year it reached 4 feet. It is in the back of the my rose bed. You can safely prune those long canes for Olivia. It won't mind at all. After all it is not a once blooming old garden rose which you dont' want to prune at this point of the year. However, if you wish to have rose bushes that stay around 3 - 4 feet with rouind shape, most Austins are not in that category. The exceptions are Munstead Wood and Boscobel, which I managed to keep around 3&1/2 feet tall. Agree with threelittlelights13 that planting in groups may help in the look. My garden is semi-gormal with a lot of boxwood which were planted 1&1/2 feet apart - now all grown together. and helped to create a more formal look. I am not sure that's what you are looking for, and perhaps you just want a neater looking garden. Nevertheless, I included a few photos below. Those in the fronts are Boscobel and Bolero which does stay wtihin 4 feet with pruning. The yellow is Julia Child which actually reached 5 feet in the spring.

I just chopped off half the growth of a 1-meter tall Mexicola Grande because it wasn't branching. I did the same thing six weeks ago to a Fuerte of the same height, and it is exploding with branches all over the place. I read a research article yesterday that was comparing top-pruning 8-year-old Hass and Fuerte trees at 4 meters and 6 meters, and the 6 meter height gave much better yields over several years. Another research article was talking about selective pruning of fruiting branches in the spring to reduce the fruit load so that you can get a fruit load on alternating years. The research has convinced me to do that eventually to my Fuerte, which is famous for needing rest years. You don't prune the whole branch, but choose several main fruiting branches per year and cut the flowering tips off of the others. The next year, you prune the previous year's fruiting branches to stimulate production of new growth, which is where the flowering for the next season will occur. You have to do this in the spring to give the tree time to establish new growth to the maturity necessary for it to differentiate into fruit wood. What concepts regarding raising your trees are you most interesting in exploring these days?