The way I see things is that the i110 accessories will increase your Strength by 90 over your base. This is more than enough extra damage. My plan when I finally get these accessories sussed out is to get Fending Accessories(like you, Strength IV is half the price of Vitality IV on my server) and toss Skill Speed III's into empty slots. That should toss me over 400 Skill Speed no matter what I'm wearing. And, regarding the whole 421 thing:

380 speed will get you the 9 hit Zerk if you really time things right.
400 speed will get you the 9 hit Zerk most of the time, even if you're late timing the buff.
420 speed makes the 9 hit Zerk almost effortless.

Of course, your personal latency must be taken into account. Figure out what number you need to make it easy and stick around it