When I bought 3076, it came with an alloy hog-stepped mast.  In the absence of anything else to compare it with, I assumed it must be a standard.  Having now seen quite a few other boats as the Scottish fleet expands, I realise that it is different.  

First it has only a little taper along the full length; the top is flat and probably still 5cm across.  Second the mast is, not surprisingly, very stiff.  I can induce some pre-bend using jib and shrouds but the kicker adds very little and there is no sign of any further 'give' in gusts up to Force 3-4. (Above that, I tend to be too busy to look) 

What have I got, and how do I get the best out of it?  I am probably sailing with a crew weight of 23-24 stone.

Is the top section coloured (Often black)? If so it's a needlespar.

If it's gold anodised it's a Proctor, by your description probably a B section. These are enormously stiff.

It also sounds like you could be the proud owner of a mast from a differant class that has had the top section cut down to make it fit your luff length. 5cm is a very large section for the top.

Photos would be helpful.