Does anyone know if i will have compatability issues with an older 7700 dura ace 9 speed hub and a new 10 sp ultegra cassete (the rest of the drivetrain is 10sp). I know i’ll need to use the spacer that comes with the cassette. But i’d heard that some dura ace freehubs had deeper splines to prevent freehub damage.

Anybody got any experience of this?

it’s the (older) 10spd DA hubs that have the alloy freehub and deep splines. The new 10spd hubs have gone ti freehubs and shallow splines.

10spd cassettes go on 9spd freehubs no problem (with the thin spacer)

As above. All 10sp cassettes will fit 9sp hubs (and newer 10sp DA ones too). Some DA and Ultegra 10sp cassettes have nice alloy carriers with deep splines for the alloy hub body, but they’ll go on all other hubs too.