Lynskey's R450 frame is made with 6Al-4V tubes and they call it their strongest frame, but the MSRP for just the frame is $5,154 (but it's on sale for $2,577).

In contrast, their R350 frame, which I believe has 3Al-2.5V tubes, has an MSRP of $3,234, but it's on sale for $2,263.

Based on the numbers, I'm just not sure a 6Al-4V frame is worth the premium, but YMMV. With both frames on sale, there's only a little over $300 difference. Hmmm...