As you are considering doing, I did the mod to stop the oil consumption.
Oil is cheap (as LJ often says) but mine had gotten to the point where it could do some damage. I was getting as bad as a quart in 250. Since I often go on long trips (multi day, a couple thousand miles) it was getting to be a real pain as I was needing to constantly check the oil and often had to top off at every fill-up.
I did the 685 and am a self-confessed experimenter and tinkerer. While I was at it I decided to go all the way with a ported head and big valves. I've also got a modified exhaust, intake, and have gone with the KLX needle. I tune with an Innovate LM-2. It could be said that I've gone the whole nine yards. I have The Most Powerful KLR In My Town™.
It's smooth and the passing power from 70-95MPH is satisfying.
Now, I have to freely admit that I believe that the biggest bang-for-your buck mod is the simple 22 cent mod. Money spent after that is analogous toThe World's Fastest Indian. The 22 cent mod gives you 10 horsepower/dollar. The 685 kit, as I did it, gives you .005 horsepower/dollar. I made those numbers up, but I'd wager that a dyno would prove me accurate if not precise. Obviously, then, the 685 should be done for oil consumption, eh?
Were I to do it over again, no I don't think I'd go for the 705. From an oil consumption perspective it doesn't solve the problem better than the 685. From a power perspective it offers even less bang for your buck. Actually, Cary Aspy died before the 705 ever got totally sorted out and from what I have read (Patman's stuff) it didn't really live up to expectations. I know the Schnitz kit and the liner are sorted out, but I never really felt that good about popping the liner and putting one in that is so thin that special heat treatment is required for it to be workable.
There's at least one member here who has done the 705; perhaps he and anyone else with first hand knowledge (rather than opinion) will chime in.