I would be ultimately pleased with a 2.0 base GCD. at 2.5 base playing as a MNK with more Skill Speed than I should have my GCD is probably at the 2.0 range and it is far more fun at that pace. If things went down to a base 2.0 with most classes reach about 1.8 and MNK/NIN at 1.5 you'd have actual fast classes to play as.

OR go in the direction of reworking Skill Speed to directly effect TP return. Then the stat would be less punishing and allow for more diversity between builds that focus on quicker hits or slower, more powerful ones.