I’d go for it - there is genuinely not much in it versus the GM L540. I used the six6 for many years and the Mythos (both L540 and both great bats). As noted above Kippax are usually ok to tweak the length anyway but for the sake of 0.5cm you’re not gonna notice it.
I emailed them my specs along with the order and what they sent (dragon) was spot on - with the option to return if unused. The press was perfect (medium/soft), paid them a tenner to get it knocked in, pinging from the off. Just one thing to note is with my one the willow was high grade low density so was picking up light. I’m going to order another one today and get it slightly (1oz) heavier. I’d say go half oz heavier and you’re in safe space. I also got the traditional handle not the wavex.