There have been a number of threads on the topic of replacement seats. I found the stock seat wanting, but then again, I've never had a bike with a stock seat I really loved. Based on the input of a few folks whose opinions I value, I ordered up a racing seat, and put it on the bike a few weeks ago.
Since putting it on, the longest ride I had done was ~70 miles. Until yesterday. There was a Bay Area Riders Forum (BARF) ride from Cordelia to Calistoga via twisties that I used as a jumping off point, from which I rode up Geysers (twisties, goat trail, and some gravel sections) and over about 20 miles of dirt road between Hopland and Kelseyville, then down to Big Canyon to Middletown, then backroads back to Cordelia again.
It was a good test of the saddle, so here's my impression:
Better than the stock saddle for long rides? No contest. The stock saddle doesn't have enough support. The racing saddle is firmer, and it supports the rider better, and it's easier to stay where one wants in the saddle, avoiding having the jewels mashed against the tank.
Is it perfect? Nope. Still pretty hard, leading to a somewhat sore butt from riding bumpy roads.
Would I do it again? Yes.
Additional feedback on the Hyper is so far so good. I picked it up in mid May. It's got about 5600 miles on it now. It left me by the side of the road two weeks ago, but the closest dealer (Munroe Motors) and DNA took care of the problem under warranty. Apparently a battery post broke.
I seem to be averaging right around 40 mpg now on California gas. Better than when I first got it. It feels like the engine has freed up a bit, but that could be my imagination. Not having any of the stalling issues folks are struggling with, so I'll count myself lucky. I'm still quite pleased with the bike.
On the topic of other accessories, I'm pleased with the DP tank cover and bag. It allows me to indulge my packrat tendencies. OTOH, the DP wind screen I bought is no more. Being a clumsy prat, I broke it

while washing the bike. I don't plan to replace it. I replaced the stock Bridgestones with Michelin Pilot Road 2's about 3K miles back. They are holding up well, and have enough stick to allow me to ride pretty quickly on the street. I may experiment with others tires, but these are quite good.