I think it's interesting looking at Dave and H's work in the 80's. The evolution:
Killers
Dave: Vintage Dave, lots of legato, a lot of Robin Trower influence.
H: Very basic solos, but very melodic.
TNOTB
Dave: Less Trower-like, still a lot of legato, but nothing new.
H: New technical things such as tapping (COTD), solos still basic, but melodic.
POM
Dave: Even less trower influence, more dive bombs, but still his signature fluid style.
H: A few new things, but nothing major. His guitar tone on this record seems like he has the tone rolled off a bit when soloing. His solos ot a bit faster.
Powerslave:
Dave: Even more divebombs. Some great melodic solos (Powerslave). His solos on this record seem more structured (IMO) on this record than on previous ones.
H: Introduction of the whammy bar with his Ibanez Roadstar is probably the biggest change here.
SIT:
Dave: Even more divebombs, less distortion and a lot of chorus, but his playing still seems like his typical playing. The solos still seem quite structured compared to earlier albums.
H: Basically a new improved version. Lots of whammy bar, lots of tapping, introduction of different kind of accenting, introduction of a lot of harmonic minor soloing.
SSOASS:
Dave: Took a leaf from H's book. Everything H did from Powerslave to SIT he did from sit to SSOASS.
H: Natural progression from SIT, maybe a bit more reserved in all aspects.
So biggest leaps: H: Powerslave to SIT and Dave SIT to SSOASS.
I might add that another big leap for H happened in the mid 90 with Psycho Motel and Accident Of Birth/TCW. Notable tracks: Rage (first time I heard H playing slide), Western Shore (H sounding like a mixture of Davey and Hendrix's manic depression), Omega (just beautiful and a few slow sweeps), Road to Hell (that thing he does at the beginning of the solo reappeared in Wicker Man), The Last Chain (Introduction of H service pack 3, aka modern H. Exposed to Ty Tabor, Jerry Cantrell and Roy Z.), Jerusalem (even more added semi tones to his playing) and Darkside Of Aquarius (semi tones, again).