To underscore what tolanj said above...
For heroics, the most effective AoE with a bastard sword is not the strikethrough, it's a cleave. IFF you have cleaves you're best off using those with a SWF weapon with a lot of damage instead of the "passive" cleave of the BSword (although a bsword is perfectly fine too). You just won't have enough strikethrough (20-60%) to make a huge difference in heroics. I hit a similar dynamic on my CHA SWF pally build and found the cleaves in KotC were vastly more important than the strikethrough. I leveled with Bsword more because I had nice bswords rather than that it was more effective than a longsword.
Assuming you just live with cleaves and take SWF, it changes at 31 when you pick up the whole THF line from your L 31 feat. Then the Strikethrough goes up to more like 240% and you actually are hitting enough to make a difference.
For the "I just want to hit things with a BSword" Arti build, you can target 18 arti/2 fighter OR 12Arti / 8 Fighter.
I'd recommend front loading fighter levels and going with with option #2. So take the next 5 levels as fighter than all the rest arti. Take 41 AP and Tier5 of Kensai, enough AP into Stalwart defender to get the first tier of the PRR Aura, then INT to hit/dmg from Harper tree as well as Know the Angles, then everything else into BE and RM. Don't worry overly much about stats, just put everythign into INT and take Harper tree. up to about 13 points.
You'll wind up with 38 odd points in Kensai, 13 points in Harper and then.... You can decide to basically ignore most of Battle Engineer beyond the first couple abilites since the Kensai tree is a way better tree for actually hitting things. In that case your points go into Defender and RM to make yourself more durable or Take everything in BE up to Tier4 and be very heavily optimized for offense. Or split the difference.
I'll try to post that build over in the arti forums since I'm about to go run it myself.