As stated above, every land and design is different but we're talking hypotheticals so my ideal is high 60's. This is for a tournament layout course and for players that want to test their abilities and play for the challenge of Disc Golf.
I'd have a couple of par 5's in there and more 4's than threes, i'd have at least one hole that Steve calls a par 2 and I call a must get par 3. I like multi shot holes though, I find them more fun than 3's if they are well designed with a distinct challenge set on each throw. I like more chances to throw great shots.
As there aren't many serious golfers or tournament level players out there, you have to design for the majority so my ideal course of 18 holes would probably be split into two loops of 12 or even 18 holes, or most likely one loop of 12 and one 18. The twelve would retain some 4's and split the par 5 and at least one four into 3's (one of the Gold threes might get redesignated into a 4 for the level of play) and the 18 would split all the 5's and 4's into distinct par threes. The 18 would be set with par around 920.
The 12 would be looking more at 950 rated The 18 would be a fun birdie fest for a good player but a challenge to the majority with chances of 2's but lots of places to mess up. I would also have a 9 or 12 hole beginner layout somewhere near the clubhouse, which would still be fun to play for experienced players.
This gives more players more chances to be on the course at the same time and gives them a helluva variety over the same bit of land. There would be a red/green, White, Blue and Gold course to play , or a mix of the three big ones. I really like hearing the question "which layout should we play today" variety is the spice of life and everyone has different time constraints and holes that appeal/don't appeal to them.
As long as planning permission is successful I'm making one like this at the moment, i'm excited to see how it comes out and Steve will be glad to hear the Golds are aimed to be set for 1000 rated play and not "British" par
I suspect the majority of rounds will be played on the British par layouts though.