So I’m trying to complete all the route badges and I’ve only got the PRL full to go. I did the Uber pretzel today and I really had to dig deep on the last quarter of the alp. My FTP is around 245 (this is backed up by my alp best being 58 minutes at 245). For the Uber I aimed to do 220 on the koms (ignoring flat/downhill sections on the koms), just keep the legs ticking over on the downhills (100-150) and 160ish on the flats. I thought this was what I did for the 4 horsemen, but looking back on strava it was actually 200 for the koms.
After the first few hairpins on the alp my plan of 220 quickly became 200 and in the end I did average 205 for the alpe and 174 for the whole Uber pretzel.
Anyway, back to the question about pacing. Is my aim of trying to go harder on the climbs a good one or should I try and keep a more even power output regardless of incline? Is there any sort of standard guideline for % of FTP to aim for for a given ride length?
When riding a longish hilly route solo, I tend to go easy/endurance pace on the flats and then tempo the climb(s). Sometimes, I’ll up the pace on each successive climb.
If you want to really push yourself, find a group ride/event doing your route. The, you can ride w/others which helps w/passing the time as well as increased motivation/ability to push the pace.

David, this generally can be determined from your Power Duration Curve (PDC). It is calculated from your past rides. The caveat is that to see at what power you can ride for 3 hours, you need to complete several 3 hour or longer rides to populate your PDC with this data. Any cycling data analysis program can calculate PDC for you from the past rides, and Zwift shows it to you, too, at the end of each ride (it is in one of the tabs which you can click on and open before you exit Zwift).
When it comes to general guidance, long rides will be a mix of endurance and tempo zones, and very long rides will be pretty much all endurance. Endurance and tempo zones can be estimated from your FTP.