I rode my 1098 from Atlanta Ga to the Indianapolis Speedway last summer for the Moto GP races. It was about 550 miles. I was comfortable up until the last hour or so when the seat started to feel really thin. I averaged about 45 mpg. I've seen 53 mpg running a bit slower with some Harley riding friends.
I realize you asked about the 1098/1198, but the ergos of the 848 are the same. Ive done a few 300+ mile days with mine. Initially I thought it was a torture rack. The bike is perfectly setup for a 30 minute session on a race track where you need to crawl from one side of the bike to the other quickly. For long rides having your knees tucked up in your armpits, your elbows hanging below your scrote and wrists bent at 120degree angles just wasnt working.
However, being stuborn and foolish I've kept on riding. At this point doing 300 miles isnt an issue. Just plan ahead and schedule occasional breaks.
Because my 848 is not a dedicated track bike I'm looking in to adding some 'comfort mods to address some of the remaining issues:
1 - the clipons have a really small diameter for my hands and they vibrate which makes things worse. I'm looking in to getting fatter grips that offer more cushion to help deaden some of the vibration. However, I don't want to deaden things up so much that I can't feel the feedback from the bike (front wheel).
2 - the stock seat isnt bad, but it could use some additional cushioning to help support my royal sephincter on long rides. Again, I don't want to compromise my ability to move around on the bike.
Finally, I was seeing 40+mpg (maybe 46mpg) on my last right. Speeds varried from boring to enthusiastic depending upon traffic and line of sight.
As a point of comparison - I find my 848 more comfortable than my ZX6. And oddly I seem to get better gas mileage.
I'll be doing a ride around lake superior from the Minneapolis area next month. It should be about 1600 miles total. We have 4 days to get it done. I rode my RC8 550 miles in one day once, and I am thinking that 4 400 mile days in a row is going to get uncomfortable fast, but we just don't have more time to do it!
I actually like the open ness of the stock pegs, my old 08 CBR 1000RR my legs were cramped even with rearsets, and my knees would ache. Ive never had knee issues on the 1198. I did add a TPO heatshield panel to cure some heat from the exhaust, helped to the tune of about 20 degrees according to my IR gun.
The only time i feel like my 1198 is a rack is right after i jump off my ST3, which i use for longer trips, and ill use the 1198 for 400 miles and under days.
Well I rode from LA to San Fran only to find out the rooms were way to expensive and after have to replace my rear tire came straight back. I'd say about 800 miles in one day. Not to comfortable on the way back with my tank bag hitting my lower back. Seriously though, twisties are way more comfortable than straight line riding for sure. Mileage, I'd say 45ish.