Belden has several products for data transmission, for e.g. they have 25 & 37 conductor low capacitance computer cable intended for RS232 RS485 etc ' low dielectric high speed low distortion data handling'.
The 9925/9938 series.
Also Individual shielded pairs 36 conductors.
Max.

I've had a look at those and they'd be perfect - just wasn't sure if there would be massive crosstalk between the bundle when running clocks along it. What is the part number for the individual shielded pairs? I've googled, but can't find it. One option is just to grab cable samples and give it a try!

 

Belden has a few types that are aimed at RS232/RS485 etc.
The one with individual shielded pairs is 89729 to 18 pair-36 cond 89758.
Max.

 

I really doubt if you would have problems with crosstalk for such a short cable, but you can buy some pretty expensive cable for a one-off installation for what it would cost to do testing - or much worse, fixing after the fact.

Without a doubt Belden makes high quality cable and I've used lots of their products. They are typically quite expensive and it can be difficult to find a distributor that well sell you cut lengths, depending on the popularity of the cable you. Most cable vendors will have a reasonable equivalent and since the application is not particularly demanding, I would expect the possibility of them not quite measuring up to Belden quality would be no issue whatsoever. I've used "house brand" cables from Allied Wire and Cable and found them quite satisfactory for mid-level performance requirements.

A cable with a pair for each signal is obviously going to be larger diameter than an unpaired cable. You aren't going to benefit significantly from the pairing for single ended signals, but cables with individually shielded single conductors are almost nonexistent (unless you count cables with a bunch of individual coax lines, and you don't even want to think about how expensive they are!).

 

I want to run a handful of RS232 bit synchronous signals between two places (So data and clock lines). Is it okay to run a load of these in a single multicore cable or do I need to run them in individual cables?

Not much guidance out there on this. But space at a premium

If it's unshielded, just make sure it's twisted pair.