The delay with an 87 speed shield is significant enough that it limits your options compared to a 100 speed shield. Harder to sneak in attacks vs. multiple opponents, harder to feint dropping your block and still recover in time, etc. However, speeds of 94+ might as well be 100. I wish there were more shields in the 90-100 speed range.
Specifically, a shield with stats averaged between the Heavy Round and Elite Cavalry would be my dream shield. 92 speed, 35 diameter, 300 HP, 18 armor, 6.5 weight.
Only downside to that shield would be the weight is low enough to allow it to be stunned by Nodachi, War Cleaver, Great Axes, Bardiches, etc. At 7.5 weight, the Heavy Round can only be stunned by 4+ weight weapons, which are fairly rare; Bar Maces, Mauls/Mallets, etc. To me, that's the most attractive aspect of being a shielder; you can block held attacks from almost anyone without fear of being block stunned, while still having a fast weapon (1h swords). Longsword may be fast, but you spend half your time unable to attack because of block stun.