The 8" SilverFlute's look like they can make it too 1700 hz.
The HI-VI TN28's will probably struggle at that crossover point and then theres that c-t-c spacing problem at 7200 hz.
According to Griffin's white paper combing will start to appear at 7200 hz and get worse at 14,000 hz.
Madmike2 was probaly thinking of the B&G midrange planars.
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=135
The first project I've ever built was my line arrays using 10 Dayton 5 1/4" Aluminum Woofers and 6 Dayton PT2 Planars. Crossed over at 2500 hz - 4th order Bessel. That was before the Dayton RS series came out.
Now I'm starting to build a line array with 10 RS 7 inchers along with 10 B&G Neo3 PDR's Planars and I'll probably cross them at 800 - 900 hz. Won't know the actual crossover until it's all put together. I'm not worried about the sensitivity mismatch of the two drivers as it will probably be a natural baffle step correction. If I do need more SPL from the planars I could always parallel more of them to get it to match the woofers.
Before the RS series came out, I was planning on using the 6 1/2" Silver Flute's with the the PT2/Yag20's (they're made by the same company).
They'res also DIY'ers out there who built line arrays with only one tweeter. They'res a point source/line array boundary problem but in a small room at seating distance it doesn't appear to affect the imaging that much.
I like to have the sound stay the same - sitting or standing and walking around the room. So go with the planars. It really depends on what you want in the end.