I'm after some new high tensile bolts for my 126s suspension and stumbled across (on eBay) some titanium ones. I'm no metallurgist and really have no clue about thses things so I was wondering if anyone knew if titanium bolts would be stronger or, more importantly suitable for use in certain areas in the suspension where high stresses are common.

It would depend on the exact composition
Steel itself is actually stronger then titanium due due a much higher density
That being said you wouldn't need to worry about them rusting

I see so is it’s strength dependant on how the load on the bolt is applied? Like lateral forces? One particular advert claimed theirs were “grade 5” and were the strongest commercially available.

Grade 5 is usually an imperial standard, similar in properties to metric 8.8. Most bolts, particularly for structural or suspension use are metric at least 10.9 which would be similar to imperial fasteners in grade 8, these specs are for carbon steel. You really want the right spec nuts for the bolts and make sure it's all torqued up right too.

Have a look at the fastener you need to replace and there should be something stamped on the head, go to a fastener supplier with it (or dimensions and a picture) and you should get it for buttons.

Cheers

Ben

As stated, suspension bolts are mostly 10.9. Only viable replacement is steel.
https://www.westfieldfasteners.co.uk/ScrewBolt_M.html
See their reference section for comparisons of tensile strength, and you'll see that the best stainless is about equivalent to 8.8. Info above suggest titanium not as good.
Use steel, others not worth the risk.

Excellent stuff guys thanks a lot

Keep well away from such things. They will break if tightened to the correct torque. Titanium is not a super strong metal. Its properties include resistance to corrosion, light weight in comparison to steel, but not high strength, which only corresponds to mild steel at best. If your wheel drops off and causes an accident, they would come under scrutiny if serious injuries or death were involved.