Effects of test patterns

Both patterns are necessary.

AA/55 causes no net bus current in the transitions, pairs of lines are effectively differential, so there's no ground current in either driver or driven ICs. Alternating FF/00 causes maximum ground pin current, so is needed to test ground bounce.

If the tracks run parallel, then AA/55 excites them in odd mode, with capacitance to ground and the mid line between tracks, making them effectively CPWG traces, lower impedance than microstrip. FF/00 excites them in common mode, so capacitance to ground only, and an even higher impedance than equivalent microstrip. It's worth testing signal integrity with both extremes of effective impedance.

From an electrical perspective AAh and 55h are preferred to test a worst case cross-talk in addition to delay effects. Testing other patterns is also beneficial for instance FFh to 00h will consider thermal stress better than AAh to 55h.