First, understand that I live in Oregon, and catch a lot of Albacore. Not BFT, not YFT. Then, to answer your question:
X-Raps, 4.5 - 5 kph
Trolled swim baits, 4 - 4.5 kph
Feathers, clones and wood, 5.5 - 6.5 kph
Archer Bars (RIP, Fred!) will troll well at any speed. FWIW my favorite spreader...