Oh no, you've opened another can of worms! Sorry to broaden this out but I can't for the life of me decide on a system. The Optech still looks great, but for me I need a wedding/events solution for two cameras and maybe a bag too! I keep coming back to the Black Rapid, but 90 quid! I guess I could trial a £10 Chinese copy and see how that feels. But I'm also thinking - shoulder bag/sling? arhgggg.

For the OP it does look like either of the Optech designs would work.

Optech strap looks the best value.
Does this sling preclude the use of a rucksack?
Does it come with enough straps for two cameras?
Would you hang a 645 on it?

Fabulous.
And what David said

I don't agree. The amount of money we are talking about isn't going to make a jot of difference to the bills coming up if the new job fails. You've got some cash; enjoy it!
No comment on the choices, except to say I love the K5 and personally, I would only buy the K3 as an addition to the K5.
Lenses are where the gains usually lie.

Yep. Not at all concerning.
I've recently bought a (fairly) wide angle film lens for my digital 645 and it performs just fine. Stars at extreme edges display a certain amount of chroma, but only when pixel peeping and certainly not a concern for the image as a whole, as the important bits are never near the edge.
It is worth remembering that film lenses are invariably designed for larger image circles than the digital sensors so the problem areas lie outside the cropped sensor. This is the case even on the 645 system.
edit: sorry, posts overlapped

Link has a dot at the end. This causes an error. Just remove the dot in your browser.
I'm inclined not to bother looking at this, because it is an tiny concern compared to just getting out and taking good pictures. But I'm curious, so I'm going in!

First lens I ordered for my K10D years ago. Never regretted it. It's a game-changer. I won't part with mine.
Here's a snap taken yesterday.

Oops! sorry this sold last week.

Cool! So did this have a tracker of any sort. If not, what settings did you use?

I just pointed the Zed and 35mm @f4 in the general direction and fired off a few under-exposed shots (to keep the shutter speed up, as I don't have any kind of tracker).
After getting home and zooming in I discovered the little green blighter on one frame
It was midnight and the comet was nearing the pollution of Plymouth, but it looks quite funky anyway I think
click on it