I did some thinking, and Vaporeon doesn't need any speed, trust me. Unless you really want to invest in speed, it's pretty unwise since you'd need Timid to even get anywhere - and that means a very low Sp. atk. Again, if you wanted a speedy Sp. atker, you'd definatly need to go with Starmie. So forget about what I said earlier, drop all speed EVs - Vaporeon's natural low speed already beats things line Tyraniboah, Weezing, and Rhydon. ..And that's about it without huge EV investment.
First of all, invest 252 in Sp. atk, ofcourse. Completely necesarry. Next, shove it all into HP. I highly recommend using wish. Now, the important thing is this - Vaporeon is very bulky this way, but without a ton of defense EVs it won't be taking Choice Banded hits, it's meant as a hit and runner basically, I'd say. It can still take nuetral non-boosted hits and hit back hard this way, which is what you'd want from an offensive Vaporeon.
Next, Sp. def EVs on a Vaporeon is virtually unheard of. All of it's weaknesses are special, so nevermind. Again, without some HP EVs Vaporeon can't take special hits either, which would require splitting your EVs further. And once again, with max HP you're recovering over 250 HP per turn with a wish. Impressive, no?
Sorry for being slow, takes time to analyze all these things for me.