one month later...
what sort of rack do you have? my surly nice rack is steel and doesn't flex "that" much, but with bags and basket loaded, it sure as hell feels as though it does. I think it's mostly the bags, but could imagine the rack swaying a slight amount. who knows. in any case, it usually takes me around fifteen minutes to get used to it and then it feels fine.
sram gear is deece. you might have to change out your shifters to get whatever new drivetrain stuff figured out. if you're using friction shifters and aren't snagging a new hub to fit more gears, chances are you'll be able to shift fine in friction mode. if you have more/less gears, then your indexing will be off so friction mode will be the default. In any case, I know more about mountain drivetrains than road. the shimano mountain 11 speed fits on normal mountain cassette hubs, whereas sram stuff does not. also, there is different pull ratios on some of sram's stuff and 11 speed shimano road things, so that's worth noting. If you're on the fairdale archer, then you probably don't use friction anyway so most the stuff above is moot.
if you're thinking about switching to a double/triple ring up front, then you miiiiight need to switch out your cranks. also, front derailleurs are super simple so you don't need to bounce on really expensive ones.