So I'll chime in on a couple things. First, that chart seems to describe pretty well where you're getting smooth running (side note: that typo! 1/38"!!! talk about a pea-shooter exhaust!). I think you know enough about your engine to pick well. I concur with the sidewinder suggestion, make sure you match the header size with new J-tubes or all will be for naught.
Your engine is an intricately linked set of systems, so be prepared to go through the timing and carb adjustments all over again to get it right for the new header and exhaust. It'll be worth it, trust me! I've assembled, built exhausts, ported, tuned and tweaked a bunch of motor cycle engines from 710cc singles, to desmo twins, to inline fours and every single one required a lot of fettling to get things right. No two were exactly the same even when built with the same kit and parts. I was lucky to have a dyno available to me for this, I would have been arrested trying to do it out on the road. (If someone already said this and I missed it, I agree, sorry to be redundant, just give me a dope slap)
A word about magazines. They are super fun, and sometimes a useful source for info, but they are written by journalists. Some of them are experts, some them are good at sounding like experts. An example: In the waining days of my motorcycle racing I was doing a lot of work with a track day group as a control-rider/instructor. This group had a deal with Aprilia to use their bikes for their instructors in return for holding PR events including press days to introduce new models. Now, I used to read these mags religiously growing up and spouting what I'd read, "There's very little front end feel at the limit on the XXX 900!" and such like. When I was riding as control-rider-embassador at these press events I found that maybe 2 out of 20 "well respected" moto-journalists could even get the bike any where near it's limits. Also, the better the lunch and post event cocktail party was, the better the bikes seemed to handle in the next issue. So enjoy the magazines (lord knows I do) but take it all with a grain of salt unless their quoting someone with known cred.